minimal clean up (unused imports, commented out code etc.)
added/updated license headers
Removed mention of obsolete Ant build. Removed link to obsolete "Building Groovy from Source" instructions. Added remark that building from Eclipse is not possible at the moment.
GROOVY-6170: Upgrade ant 1.9.0 -> 1.9.1
ignore "bin" directory (created by Eclipse)
GROOVY-5344 - Update jline dependency

update Eclipse classpath for new jline and jansi versions
GROOVY-6172: bump testng dependency 6.8 -> 6.8.5
GROOVY-6173: bump xstream dependency 1.4.2 -> 1.4.4
GROOVY-6173: bump xstream dependency 1.4.2 -> 1.4.4
GROOVY-6095: Workaround for generics type checking bug