Added mercurial plugin with aliases.

plugins/mercurial/mercurial.plugin.zsh

+
+# Mercurial
+alias hgc='hg commit -v'
+alias hgb='hg branch -v'
+alias hgba='hg branches'
+alias hgco='hg checkout'
+alias hgd='hg diff'
+alias hged='hg diffmerge'
+# pull and update
+alias hgl='hg pull -u -v'
+alias hgp='hg push -v'
+alias hgs='hg status -v'
+# this is the 'git commit --amend' equivalent
+alias hgca='hg qimport -r tip ; hg qrefresh -e ; hg qfinish tip'