Add "has" method, to check parameter existence.

Can be useful since the real parameters map is protected.
Use java boolean
Allow developers to provide their own implementation for AsyncHttpRequest.
Merge pull request #560 from ebuildy/patch-1

Add "has" method, to check parameter existence.
Merge pull request #564 from fineswap/AsyncHttpRequest

Allow developers to provide their own implementation for AsyncHttpRequest.
Updated Javadocs to get valid build output
Updated build configuration for latest Android SDK distribution package
updated Travis configuration