Implements `Encodable` and `Decodable`

Fixes #27
Merge pull request #29 from gifnksm/master

Implements `Encodable` and `Decodable`
Add numeric functions and `traits` module that provide numeric traits for generic
mathematcs.

Import numeric traits and functions that were removed from the standard library.
This also implements `AdditiveIterator` and `MultiplicativeIterator` for
`BigUint` and `BigInt`.

closes #28
Add `iter` modules for generic number iteration.

The codes are imported from the standard library.
std::from_str::FromStr -> std::str::FromStr
Merge pull request #30 from gifnksm/master

Add numeric functions and traits that provide numeric traits for generic mathematics.
Fix for namespaced enums.
Merge pull request #31 from gifnksm/master

Fix for namespaced enums.
Bump to 0.0.2
Add crates.io metadata to Cargo.toml.
Bump to 0.0.3.
use crates.io in README
Merge pull request #33 from steveklabnik/master

use crates.io in README
Update tests to rust master
Add keywords to cargo metadata.
Update to iter stabilization.

`AdditiveIterator::sum` and `MultiplicativeIterator::product` now take bare self.
Merge pull request #34 from gifnksm/master

Update to iter stabilization.
Bump to 0.0.5.
remove license attribute
don't allow deprecated items.

We don't actually use any.