Replace pid check with thread id check.
Added some threaded ping tests.
Skip most tests if JRuby.
Updated known issues for ICMP.
Added note about ICMP thread safety.
XOR the current thread id with the current pid, just to make sure there's no conflict between processes.
Bumped version, minimum Ruby version.
Added note about required minimum version.
Updated copyright, project page.
Added a release date.
Version bump.
Merge remote-tracking branch 'djberg96/master' into try_djberg96

Conflicts:
	README
	test/test_net_ping_icmp.rb