error_chain macro does not support doc strings

[heartsucker]

This makes using #![deny(missing_docs)] impossible at the crate level.

error: no rules expected the token `;`
  --> src/error.rs:12:1
   |
12 | / error_chain! {
13 | |     foreign_links {
14 | |         /// Foo bar baz
15 | |         ChronoParse(chrono::ParseError);
...  |
48 | |     }
49 | | }
   | |_^
   |
   = note: this error originates in a macro outside of the current crate

[Yamakaky]

Duplicate of #63.