Merge pull request #626 from Morwenn/constexpr

Constexpr
Use a different SDL_RWops for each font size.
Update sample quest, initial quest and testing quest fonts.
Remove useless destructor.
Fix compilation issue due to missing constexpr.
Work in progress: new function surface:get_pixels().
Reindent tests cmake file.
The testing quest can now run without error.
Unit tests can now be written in Lua.
Merge branch 'lua_pixels'
Add a unit test for surface:get_pixels().
Only initialize hqx at first use.

This initialization is very long in debug (0.5s on my machine), which is
far from ideal for each unit test.
Editor: When non-existent tiles are removed, show a more detailed warning.
Editor: add keyboard shortcuts and menu items on tile patterns.
Editor: show keyboard shortcuts in menu items.
This change was backported to 1.3.
Fix bug in Crystal::activate.
Merge pull request #627 from Morwenn/loop_fix

Fix bug in Crystal::activate.
Editor: fix custom entity editor dialog not opening if invalid sprite.
Editor: better handle tiles with invalid sizes.

A tile on a map can have an invalid size (i.e. not a multiple of its
pattern size) if the pattern was changed in the tileset.