Accept semver with and without hyphen

Trying to work around the problems of changed version spec in PGXN.

With the current sever implementation, both pgmp==1.0.0b3 and pgmp==1.0.0-b3
work. But neither plv8==1.1.0beta1 nor plv8==1.1.0-beta1 do. The server
reports a "not found" on http://pgxn.org/dist/plv8/1.1.0-beta1/ but the
url without the hyphen works.

Closes issue #22
Added SemVer repr
Try to work around 'Resource not found' in the server

Currently http://pgxn.org/dist/plv8/1.1.0-beta1/ doesn't work but without
hyphen in the version it does.

https://groups.google.com/group/pgxn-users/browse_thread/thread/e41fbc202680c92c
Report closure of issue #19 in changelog
Report closure of issue #22 in changelog
Merge branch 'semver-mess' into maint-1.2

Conflicts:
	CHANGES