Added "Converting a formatted date to a Unix timestamp and vice versa" recipe

Added "Converting a formatted date to a Unix timestamp and vice versa" recipe

src/basics.md

@@ -27,6 +27,7 @@
 | [Check number of logical cpu cores][ex-check-cpu-cores] | [![num_cpus-badge]][num_cpus] | [![cat-hardware-support-badge]][cat-hardware-support] |
 | [Obtain backtrace of complex error scenarios][ex-error-chain-backtrace] | [![error-chain-badge]][error-chain] | [![cat-rust-patterns-badge]][cat-rust-patterns] |
 | [Measure elapsed time][ex-measure-elapsed-time] | [![std-badge]][std] | [![cat-time-badge]][cat-time] |
+| [Convert date to UNIX timestamp and vice versa][ex-convert-datetime-timestamp] | [![chrono-badge]][chrono] | [![cat-date-and-time-badge]][cat-date-and-time] |
 | [Convert a local time to an another UTC timezone and vice versa][ex-convert-datetime-timezone] | [![chrono-badge]][chrono] | [![cat-date-and-time-badge]][cat-date-and-time] |
 | [Display formatted date and time][ex-format-datetime] | [![chrono-badge]][chrono] | [![cat-date-and-time-badge]][cat-date-and-time] |
 | [Parse string into DateTime struct][ex-parse-datetime] | [![chrono-badge]][chrono] | [![cat-date-and-time-badge]][cat-date-and-time] |
@@ -1294,6 +1295,34 @@ fn main() {
 }
 ```
 
+[ex-convert-datetime-timestamp]: #ex-convert-datetime-timestamp
+<a name="ex-convert-datetime-timestamp"></a>
+## Convert date to UNIX timestamp and vice versa
+[![chrono-badge]][chrono] [![cat-date-and-time-badge]][cat-date-and-time]
+
+Converts a date given by [`NaiveDate::from_ymd`] and [`NaiveTime::from_hms`]
+to [UNIX timestamp] using [`NaiveDateTime::timestamp`].
+Then it calculates what was the date after one billion seconds
+since January 1, 1970 0:00:00 UTC, using [`NaiveDateTime::from_timestamp`].
+
+```rust
+extern crate chrono;
+
+use chrono::{NaiveDate, NaiveDateTime};
+
+fn main() {
+    let date_time: NaiveDateTime = NaiveDate::from_ymd(2017, 11, 12).and_hms(17, 33, 44);
+    println!(
+        "Number of seconds between 1970-01-01 00:00:00 and {} is {}.",
+        date_time, date_time.timestamp());
+
+    let date_time_after_a_billion_seconds = NaiveDateTime::from_timestamp(1_000_000_000, 0);
+    println!(
+        "Date after a billion seconds since 1970-01-01 00:00:00 was {}.",
+        date_time_after_a_billion_seconds);
+}
+```
+
 [ex-format-datetime]: #ex-format-datetime
 <a name="ex-format-datetime"></a>
 ## Display formatted date and time
@@ -1497,8 +1526,12 @@ fn main() {
 [`Mutex`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html
 [`MutexGuard`]: https://doc.rust-lang.org/std/sync/struct.MutexGuard.html
 [`NaiveDate`]: https://docs.rs/chrono/*/chrono/naive/struct.NaiveDate.html
+[`NaiveDate::from_ymd`]: https://docs.rs/chrono/*/chrono/naive/struct.NaiveDate.html#method.from_ymd
 [`NaiveDateTime`]: https://docs.rs/chrono/*/chrono/naive/struct.NaiveDateTime.html
+[`NaiveDateTime::from_timestamp`]: https://docs.rs/chrono/*/chrono/naive/struct.NaiveDateTime.html#method.from_timestamp
+[`NaiveDateTime::timestamp`]: https://docs.rs/chrono/*/chrono/naive/struct.NaiveDateTime.html#method.timestamp
 [`NaiveTime`]: https://docs.rs/chrono/*/chrono/naive/struct.NaiveTime.html
+[`NaiveTime::from_hms`]: https://docs.rs/chrono/*/chrono/naive/struct.NaiveTime.html#method.from_hms
 [`Normal`]: https://doc.rust-lang.org/rand/rand/distributions/normal/struct.Normal.html
 [`num_cpus::get`]: https://docs.rs/num_cpus/*/num_cpus/fn.get.html
 [`Output`]: https://doc.rust-lang.org/std/process/struct.Output.html
@@ -1542,3 +1575,4 @@ fn main() {
 [RFC 3339]: https://www.ietf.org/rfc/rfc3339.txt
 [twitter hashtag regex]: https://github.com/twitter/twitter-text/blob/c9fc09782efe59af4ee82855768cfaf36273e170/java/src/com/twitter/Regex.java#L255
 [uniform distribution]: https://en.wikipedia.org/wiki/Uniform_distribution_(continuous)
+[UNIX timestamp]: https://en.wikipedia.org/wiki/Unix_time

src/intro.md

@@ -45,6 +45,7 @@ community. It needs and welcomes help. For details see
 | [Check number of logical cpu cores][ex-check-cpu-cores] | [![num_cpus-badge]][num_cpus] | [![cat-hardware-support-badge]][cat-hardware-support] |
 | [Obtain backtrace of complex error scenarios][ex-error-chain-backtrace] | [![error-chain-badge]][error-chain] | [![cat-rust-patterns-badge]][cat-rust-patterns] |
 | [Measure elapsed time][ex-measure-elapsed-time] | [![std-badge]][std] | [![cat-time-badge]][cat-time] |
+| [Convert date to UNIX timestamp and vice versa][ex-convert-datetime-timestamp] | [![chrono-badge]][chrono] | [![cat-date-and-time-badge]][cat-date-and-time] |
 | [Convert a local time to an another UTC timezone and vice versa][ex-convert-datetime-timezone] | [![chrono-badge]][chrono] | [![cat-date-and-time-badge]][cat-date-and-time] |
 | [Display formatted date and time][ex-format-datetime] | [![chrono-badge]][chrono] | [![cat-date-and-time-badge]][cat-date-and-time] |
 | [Parse string into DateTime struct][ex-parse-datetime] | [![chrono-badge]][chrono] | [![cat-date-and-time-badge]][cat-date-and-time] |
@@ -162,6 +163,7 @@ community. It needs and welcomes help. For details see
 [ex-check-broken-links]: net.html#ex-check-broken-links
 [ex-check-cpu-cores]: basics.html#ex-check-cpu-cores
 [ex-clap-basic]: app.html#ex-clap-basic
+[ex-convert-datetime-timestamp]: basics.html#ex-convert-datetime-timestamp
 [ex-convert-datetime-timezone]: basics.html#ex-convert-datetime-timezone
 [ex-crossbeam-spawn]: concurrency.html#ex-crossbeam-spawn
 [ex-csv-delimiter]: encoding.html#ex-csv-delimiter