move to gradle :
- remove lib, include jstackalloc as source, download lib from maven central
- disable instrumentation (ant-task) => unusable lib
- follow src/{main,test}/java directory layout
- move demo under test (source and dependency lib)
refactor: organize/clean imports, remove unused variables, fields
add patches from jme (https://code.google.com/p/jbullet-jme/source/browse/#svn%2Fbranches%2Fjbullet)