ref #68 - fixes thread safety for PojoMetadata cache.
Finalizing properties on PojoMetadata
optimized caching using ReentrantReadWriteLock
Merge branch 'master' into issue-68-thread-safety

Conflicts:
	core/src/main/java/org/sql2o/reflection/PojoMetadata.java
Merge pull request #69 from aaberg/issue-68-thread-safety

Issue 68 thread safety