v0.2.13

This version is finally beta-compatible.

This introduces a slight incompatibility, namely, due to the rewired reexport for chrono::Duration (which now comes from crates.io time crate).

Added

• The optional dependency on rustc_serialize and
  relevant Rustc{En,De}codable implementations for supported types has been added.
  This is enabled by the rustc-serialize Cargo feature. (#34)

Changed

• chrono::Duration reexport is changed to that of crates.io time crate.
  This enables Rust 1.0 beta compatibility.