add release test to ensure Jira tickets are in Changes

A release test will generate into xt/ that checks that any Jira ticket
metioned in the commit history since the last tag is also mentioned in
the latest section of the Changes file.
revert incomplete work on PERL-233
updated Changes in preparation for release
avoid generating boilerplate Pod for private packages
PERL-341 add installation instructions document
remove pseudo-pod directives from private packages
PERL-317 clarify documetation about thread support
add Changes entry for PERL-341
PERL-320 deprecate low-level MongoDB.pm functions
amend installation instructions
make bulk API remove/remove_one return invocant
make merge_result private
document new classes for Bulk API
ensure Pod gets right encoding directive
Change bulk API terminals to return undef

For consistency with the fluent API and other drivers, terminal
operations (e.g. insert, update_one, etc.) now have an empty
return rather than returning the invocant.
update authors in Makefile.PL
actually remove commented-out hard-coded darwin ccflags, etc.
fail configuration on OpenBSD without libpthread
Commit Changes and bump $VERSION
PERL-349 mark thread join test under find_master as TODO