Add UUID support to libextra

- generate random UUIDs
- convert to and from strings and bytes
- parse common string formats
- implements Zero, Clone, FromStr, ToStr, Eq, TotalEq and Rand
- unit tests and documentation
- parsing error codes and strings
- incorporate feedback from PR review

Author: gavinb

src/libextra/extra.rs

@@ -103,6 +103,8 @@ pub mod semver;
 pub mod fileinput;
 pub mod flate;
 pub mod hex;
+pub mod uuid;
+
 
 #[cfg(unicode)]
 mod unicode;