Since meson 0.43.0 (below our current requirement), 'symbol_prefix'
argument of gnome.generate_gir() allows an ordered list. If I prepend
'gimp_ui', it makes any gimp_ui_*() function to not start with 'ui_'.
In particular, GimpUi.ui_init() becomes GimpUi.init() which is much less
redundant.
Plug-ins that work from different bindings probably want to use their
own list-type to specify arguments, rather than working with a more
cumbersome `GimpValueArray`.
This new API should make it less verbose. For example:
```
args = Gimp.ValueArray.new(5)
args.insert(0, GObject.Value(Gimp.RunMode, Gimp.RunMode.NONINTERACTIVE))
args.insert(1, GObject.Value(Gimp.Image, image))
args.insert(2, GObject.Value(Gimp.Drawable, mask))
args.insert(3, GObject.Value(GObject.TYPE_INT, int(time.time())))
args.insert(4, GObject.Value(GObject.TYPE_DOUBLE, turbulence))
Gimp.get_pdb().run_procedure('plug-in-plasma', args)
```
becomes
```
Gimp.get_pdb().run_procedure('plug-in-plasma', [
GObject.Value(Gimp.RunMode, Gimp.RunMode.NONINTERACTIVE),
GObject.Value(Gimp.Image, image),
GObject.Value(Gimp.Drawable, mask),
GObject.Value(GObject.TYPE_INT, int(time.time())),
GObject.Value(GObject.TYPE_DOUBLE, turbulence),
])
```
There is no reason to limit it to "xhtml" only. Even more, in all
browsers I tried, the exported page was failing to load with the '.xtml'
extension, while it loads fine when renamed as '.html'.
Only problem is that now we have 2 plug-ins able to save as html (other
is file-html-table) and the first in the procedure list (with no
explicit logics right now) will just shadow the next one. We will have
to add some generic infrastructure to allow people to choose favorite
load/export plug-ins, probably in Preferences, next to the raw plug-in
selection.
