Added credit api.
Refactored java padding scheme.
Inclusion of libs mjson and retrofit (rest client).
Updated README. For detailed usage information user is now redirected to developer's site.
updated API entry points
Added new configuration and customization options.
Added javadoc comments.
Fixed tests.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	java-api/pom.xml
	java-api/src/main/java/com/xapo/utils/json/JsonMarshaller.java
	java-api/src/test/java/com/xapo/utils/json/JsonMarshallerTest.java
They are not necesary any more. Oficial api almost done
Fixed. not yet 100% functional
Fixed credit API.
Fixed and normalized payment types.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	java-api/src/main/java/com/xapo/sdk/API.java