Use ::std::result::Result to make macro hygienic.
I ran into an error using
```
struct Error {}
pub type Result<T> = ::std::result::Result<T, Error>;
arg_enum!{
....
}
~~~
Attached is a fix.
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Passing empty values, such as `--feature ""` now stores the empty string
correctly as a value (assuming empty values are allowed as per the arg
configuration)
Closes#470
Now if the terminal size is too small to properly wrap the help text
lines, it will default to just wrapping normalling as it should.
This is determined on a per help text basis, so because the terminal
size is too small for a single argument's help to wrap properly, all
other arguments will still wrap and align correctly. Only the one
affected argument will not align properly.
Closes#453
The `help` subcommand can now accept other subcommands as arguments to
display their help message. This is similar to how many other CLIs
already perform. For example:
```
$ myprog help mysubcmd
```
Would print the help message for `mysubcmd`. But even more, the `help`
subcommand accepts nested subcommands as well, i.e. a grandchild
subcommand such as
```
$ myprog help child grandchild
```
Would print the help message of `grandchild` where `grandchild` is a
subcommand of `child` and `child` is a subcommand of `myprog`.
Closes#416
By default `clap` now automatically wraps and aligns help strings to the
term width. i.e.
```
-o, --option <opt> some really long help
text that should be auto aligned but isn't righ
t now
```
Now looks like this:
```
-o, --option <opt> some really long help
text that should be
auto aligned but isn't
right now
```
The wrapping also respects words, and wraps at spaces so as to not cut
words in the middle.
This requires the `libc` dep which is enabled (by default) with the
`wrap_help` cargo feature flag.
Closes#428
