Using meson to build open-isns, add a pkg config file, and bug fixes

• Enable meson for building open-isns, deprecating autoconf/make (though the current build system still works)
• Add a package config file for libisns, so other software can find it
• Fix some compiler warnings and spelling errors
• Make IPv6 default socket type
• Fix isnsadm parsing of some arguments

Consolidate small bug and compiler fixes with small bug fixes

This release fixes a couple of small bugs, and cleans up compilation warnings/errors that newer compilers have uncovered.

Working with IPv6, with new Python-based test suite

This release incorporates some bug fixes. One was a nasty memory corruption bug introduced recently. Also, IPv6 connections had one bug which was fixed. Lastly, the perl test suite is being replaced by Python3-based tests using the unittest package framework.

All test (perl and python) pass, both with and without security enabled. Note that the perl tests are now deprecated and will be removed in a future release.