Added JVM GC checks

Added the following metric checks gc_old_count, gc_young_count, heap_used.
Added the correct UNIT parameter to other stats.

Incremented the version to 1.0.3
PEP8 specifies a maximum line length of 79 characters (more pragmatically, this is unreadable in my editor). I think the alignment change makes sense, but the first string segment ("A ") should be dropped to the next line to limit the total line length.