JSON parameter encoding no longer has options

For now, ParameterEncoding.JSON doesn't have options anymore... this
updates the documentation to reflect that.

Fixes #86
Adding .gitignore
Adding URLStringConvertible protocol
[Issue #106] Adding macosx to SUPPORTED_PLATFORMS for framework target
gs
Auditing implicitly unwrapped optionals
Refactoring multi-conditional if statement to switch statement
Auditing implicitly unwrapped optionals
Adding Xcode Playgrounds to .gitignore
Merge pull request #93 from johngibb/patch-1

JSON parameter encoding no longer has options
Adding URLRequestConvertible protocol
Adding request method that takes URLRequestConvertible
Adding Serializer typealias and changing closure signature for serializers to omit error argument
Auditing implicitly unwrapped optionals
Changing Manager.request method to take URLRequestConvertible parameter