Java 1.6 compatibility

Extending backwards compatibility to Java 1.6. The unit tests [https://github.com/stleary/JSON-Java-unit-test] still require Java 1.8. Includes the following commits:

Pull Request	Description
#195	Java 1.6 compatibility
#188	Fix negative zero
#186	Update README with number information
#185	change to public: write(writer, indentfactor, indent)
#180	Remove executable bit
#179	Update JavaDoc for JSONObject Constructors

JSONObject and JSONArray initialization with generics

Support initializing a JSONObject with Map<?,?> and JSONArray with Collection<?>.
Includes the following commits:

Pull request	Description
#168	Update Readme for Maven release
#160	Fixe possible NullPointerException
#159	Properly override Exception class
#153	JSONObject and JSONArray initialization

Update Maven central repository with recent code changes

Code changes since the most recent Maven release (20141113):

Existing feature enhancements	Pull request
New methods for Enum type	#140
BigDecimal and BigInteger methods	#135
Iterable JSONArray	#132
Remove compiler cast warnings	#122
JavaDoc fix in CDL	#120
Fix for JSONML.toString()	#118
Fix for JSONArray.toString()	(direct commit) d6ba318