3.8.0:

* Dialogs chapter: Add Non-modal AboutDialog section.
  (Kjell Ahlstedt)
* Fix some details in the Clipboard chapter.
  (Kjell Ahlstedt)
* Add some info to the custom/custom_container example.
  (Kjell Ahlstedt)
* Add "Multi-threaded programs" chapter.
  (Chris Vine) Bug #512348
* Builder examples: Update the Glade files to gtkmm3 status.
  (Kjell Ahlstedt)
* Update the description of Box to gtkmm3 status.
  (Kjell Ahlstedt)
* Fix the box example.
  (Kjell Ahlstedt)
* Fix the book/application/app_menu example.
  (Kjell Ahlstedt) Bug #683645 (Tom Jaeger)
* Clipboard and Socket examples: Make them non-unique.
  (Kjell Ahlstedt) Bug #681323.
* Basics, Simple Example: Synchronize code and description.
  (Kjell Ahlstedt) Bug #681323.
* I18n and L10n chapter: Fix broken links.
  (Kjell Ahlstedt) Bug #680546.
* gmmproc: _WRAP_METHOD: Include docs on wrapping methods with slots.
  (José Alburquerque) Bug #688587
* gmmproc: _WRAP_CTOR: Document the new "errthrow" extra argument option.
  (José Alburquerque)
* gmmproc: _WRAP_METHOD: Document gmmproc's output parameter functionality.
  (José Alburquerque)
* gmmproc: _WRAP_VFUNC: Add the errthrow optional parameter documentation.
  (José Alburquerque)
* Fix 'make check' with the latest versions of glib and glibmm.
  (Kjell Ahlstedt)