[scribus] Scribus Plugins API v2

[ale rimoldi]

good evening

at the recent LGM i've shortly presented to jean the plugins API i'm
working on.

based on his feedback and some plans i already had i've reworked my
proposal:

- it now uses namespaces
- it does not expose Qt containers to the plugins but uses as much
  as possible the c++11 ones (based on the good practice proposed by
  https://www.youtube.com/watch?v=uZ68dX1-sVc (Effective Qt (2017
  edition); see slides 10 and 11)

the code is here:

https://github.com/aoloe/scribus-plugin-API/tree/namespaces
(it's not in master yet, have a look at the "namespaces" branch)

the generated documentation can be found here:
http://impagina.org/dox/api-namespaces/
(you can compare it to the first draft: http://impagina.org/dox/api)

the ne API in use in the "new-api" branch of the applyStyle plugin:

https://github.com/aoloe/scribus-plugin-applyStyle/tree/new-api

comments and suggestions (and help!) are very welcome!

the new proposal is "smaller" than the first one and i will extend it
step by step, while porting the epub and TOC plugins to the new API.
this will probably happen next week.

finally, for those who have missed my first message about the plugins
API, the goal is to provide a high level and documented interface to the
scribus code, that make it easy (or at least easier) to create
C++ plugins for scribus.

have a wonderful weekend
a.l.e