Pattern for IPv6 addresses.

First set of tests.
Roll out the pattern.

Don't use (?:$IPv6unit{$style}$sep){4}, as that prevent one from capturing
the individual units.
Add tests for {-keep} and {-sep}
Added some caching.
Document {net}{IPv6}
Merge branch 'ipv6'

Conflicts:
	lib/Regexp/Common/net.pm
Version numbers and Changes entry.
Add new test file to MANIFEST
Ignore *.tar.gz files