pidgin/pidgin

Clean up some random gtk-doc warnings in libpurple's documentation

Testing Done:
Ran `ninja libpurple-doc` locally, verified the warnings went away.

Reviewed at https://reviews.imfreedom.org/r/585/
subdir('libpurple')
subdir('protocols')
if ENABLE_GTK
subdir('pidgin')
else
pidgin_doc = []
endif
if enable_consoleui
subdir('finch')
else
finch_doc = []
endif
alias_target('doc', libpurple_doc, protocols_doc, pidgin_doc, finch_doc)