start 0.3.0
refactor of GetJreTask

- fix some gradle cache issue  due to @Input + Custom type (should fix
#6)
- keep download tar.gz for debug, avoid re-download
- add logger.debug
- use ant.move (vs File.rename) to failed if issue and try several way
to rename (including File.rename)
fix findJreDirNameInTar when jv.update < 10
generate working launcher.exe or launcher.vbs for windows

+ no longer failed if launch4jCmd is undefined (in this case generate a
.vbs)
update README

fix #4
try to provide a better message error when getdown is apply with application plugin

but only work if 'application' is applied before 'getdown' like

apply plugin: 'application'
apply plugin: 'net.alchim31.getdown'

fix #4