Fix gen-api-gtkdoc.py to also parse an enums detailed description, which may contain a `since` attribute.
This makes the enums documentation and `Since` attribute end up in the final .gir file.
Fix gen-api-gtkdoc.py to also parse a structs detailed description, which may contain a `since` attribute,
and to generate a gtkdoc definition for those structs in the output wp-gtkdoc.h.
This makes the structs documentation and `Since` attribute end up in the final .gir file.
Let g-ir-scanner parse the original headers for the C signatures
and just add the gtk-doc comments in the generated wp-gtkdoc.h file
Also cleanup a bit gen-api-gtkdoc.py and make it omit printing most of the
whitespace clutter that it used to print inside the gtk-doc comments
* Use custom_target() instead of configured shell scripts
* Do not copy all the .rst files in the build directory
* Setup dependencies between targets
* Tidy up dependencies lookup
* Remove unused files
* Upgrade Doxyfile to the latest version and cleanup used options
