Misago 0.5.2

This release is bugfix release for Misago 0.5 line that corrects following issues:

#314 - Encode emails to UTF-8 before making MD5 of them
#322 - Don't crash when user clicks "unwatch thread" repeatedly
#325 - Make attachment keys unique.
#327 - Links to attachments are absolute instead of relative
#330 - Links to mentioned users are absolute instead of relative