This is the first step, it is far away from being complete.
Add make target "api-doc" to generate the reference documentation.
Add documentation comments to a few functions.
Move basic plugin documentation from plugindata.h to doc/plugins.dox.	       


git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@2263 ea778897-0a13-0410-b9d1-a72fbfd435f5