Added explicit width values for first and second
table columns corresponding to "Recipe" and "Crates".
Please note that this is a broad CSS style for all tables
which will break any non TOC tables.
For a cleaner solution we would need to explicitly
add class attribute to the generated HTML.
resolves: https://github.com/brson/rust-cookbook/issues/42
Added theme/book.css. It is a direct copy of the standard mdbook
book.css file with one addition of `width: 100%;` to the `table` style.
Infortunately mdbook allows only to substitute whole book.css.
Moreover please note that due to https://github.com/azerupi/mdBook/issues/227
`theme` directory has to be placed at the project root instead of `src`
