Update compression type from gzip to zlib

Weechat changed the default keyword to zlib.  We should match this
change as well.
Add support for _nicklist_diff command

Weechat now sends diffs instead of full nicklist messages where
appropriate.  This was "forced" on clients in version 0.4.1-dev,
commit 86a8b9fb.

http://git.savannah.gnu.org/gitweb/?p=weechat.git;a=commitdiff;h=86a8b9fb
Update pom.xml to work with latest android tools

aapt moved, so we need a newer version of the android-maven-plugin to
build properly.