Lib: Set default java stack size to 512k.
Fixes #22.
Lib: Increase child process buffer size

Default buffer size (200k) is too small for large amounts of
validation output. 20MB should be enough for anyone.

Closes #24
Lib: Quote the 'jar' argument to allow spaces in the path

Fixes #23
1.3.0
Merge pull request #1 from jzaefferer/master

sync with jzaefferer:master