This commit basically just moves stuff from tm_ctags_wrappers.c/h to
ctags. The "api.h" file has been renamed to "ctags-api.h" to make it
clearer it belongs to ctags when included.

The code also tries to completely isolate ctags from the caller;
previously we were using tagEntryInfo to pass information to Geany. This
however required including entry.h which added lots of other stuff we
don't want in the API. Instead create an auxiliary struct that holds
all the needed information from tagEntryInfo (currently only the stuff
used by Geany) and copy all the info from tagEntryInfo before invoking
the callback.