Quick fix for the jdk8 ea build stuff .
Restore JFX_DIR workaround
More robust check. Also should be jdk9-proof (to the extent that
it will first check that it is jdk8 before checking the build number)
Moving Getting Started doc to Wiki.

See https://github.com/jruby/jrubyfx/wiki/Getting-Started
Merge pull request #31 from edubkendo/early-access-fix

Quick fix for the jdk8 ea build stuff .
Merge branch 'master' of github.com:jruby/jrubyfx