Add --help and --version command line flags

Closes #899
Display a warning when the --game flag is omitted
Reduce scope for a variable
Merge pull request #902 from hansjoachim/reduced-scope

Reduce scope for a variable
Update engine.pl.po

Eliminating last mistakes in translation
Merge pull request #904 from Pawonashi/patch-8

Update engine.pl.po
Merge pull request #901 from dorkster/cmd_line_help

Add some command line documentation
Don't show default game warning when using --help or --version
Merge pull request #905 from dorkster/fixes

Don't show default game warning when using --help or --version
Display the default game warning on the title screen

Closes #896
Merge pull request #906 from dorkster/fixes

Display the default game warning on the title screen
Handle absolute paths for BINDIR in CMakeLists.txt

Looks like this was accidently removed when splitting the CMake file
between engine and game data.
Merge pull request #907 from dorkster/cmake

Handle absolute paths for BINDIR in CMakeLists.txt
Load only last hero_options.
Merge pull request #909 from igorko/fixes

Load only last hero_options.
Allow translating default hero names

Also, I moved the newline outside of the "Next Level:" string in Power
tooltips. This is because it messed up po/pot generation.
Merge pull request #910 from dorkster/fixes

Allow translating default hero names
Rendering refactor:
* Move API related code to SDLRenderingDevice
* Wrap SDL_Surface and positioning into Sprite class
* Move all rendering to rendering device
Rename Sprite::map_pos to Sprite::dest
Remove unused prio
Merge remote-tracking branch 'remotes/upstream/master' into rendering