implement pre_advance event

pre advance event fires before the user sees the advancement dialog.
Implements fr https://gna.org/bugs/?21464
Merge pull request #264 from gfgtdf/preadvance

implement pre_advance event (https://gna.org/bugs/?21464)
updated Lithuanian translation
updated Slovak translation
Set travis back to the usual, nonsegfaulting configuration for gcc

This reverts commit c9c75e9933c2b94cd7a965200eae42970b541867.
and commit c9c75e9933c2b94cd7a965200eae42970b541867
wmltools GUI: remove -f and -p wmllint options, add -m
fixup ab0dc2466dde77b938b6a86608f66c14634b0f7b
clean up syntax
added support for a shuffle key in  the [music] music to allow selecting between random and non-random music play
added modifications to changelog
shuffle sides based on the settings value

Before, it was based on the preference value. This was a problem when not using the mp_configure dialog (sp)
Merge pull request #265 from Zappaman/music_shuffle_feature_2

add option to not shuffle music, see https://gna.org/bugs/?19653
Add submerge and color modulation shader attributes.
Don't limit color modulation to the [-128, 127] range.
Properly set shader attributes in rectangle draw functions.
Fix sdl::timage copy ctor.
Consistent naming pattern for shader variables.
Exception for shader errors.
Add an exception for SDL_gpu errors.
Implement submerging in SDL_gpu builds.