Allow DataParser to return typed objects

DataParser should not be required to return Any and have objects checked for type safety at runtime. This allows us to use the Swift build time type checking system with very minimal changes to existing code. The only API breaking change is that Request classes using the default JSONDataParser should now conform to JSONRequest, instead of just Request. This is because protocol extensions cannot declare default associated types.

Merge pull request ishkawa#224 from ishkawa/release/3.1.2

Release 3.1.2

Merge pull request ishkawa#219 from ishkawa/release/3.1.1

Release 3.1.1

Merge pull request ishkawa#216 from ishkawa/release/3.1.0

Update version to 3.1.0

Merge pull request ishkawa#211 from ishkawa/release/3.0.0

Release 3.0.0

Merge pull request ishkawa#208 from ishkawa/update-podspec-beta-2

Update podspec for 3.0.0-beta.2

Merge pull request ishkawa#194 from ishkawa/si-swift3

Swift 3 support

Set version 2.0.5

Set version 2.0.4

Set version 2.0.3