Merge tag 'v0.25.0' into archlinux

Alpha 25
The audio_file classes (wav, ogg, opus) represent audio files.

- audio_file is an abstract base class that holds the audio data and info.

- each derived class loads the data in its constructor.

- currently the old code is used for the loading.
Audio file factory

The audio_file_factory class has one static method that returns a
std::unique_ptr<audio> that points to a wav_file, ogg_file or
opus file depending on the extension of the provided filename.
Changed the name of bit_depth to byte_depth

The name was changed because bit_depth was inaccurate.
The value is the actual bytes.
Audio file returns const pointer

Changed the void pointer that is returned by audio_file.get_audio_data()
to const void.
Remove MusicSound

Since the file system does not support partially loading a file
MusicSound does not have any uses. Its functionality is now
part of LoopingSound.
Remove the audio_file hierarchy

Removed the audio_file (and {wav,ogg,opus}_file} in favor of a simpler
AudioData struct, which contains the relevant audio data. Reduce the
audio_file_factory to functions that return AudioData objects.
Update CMakeLists.txt
AudioData now deletes any memory it owns.

If rawSamples* is owned by an AudioData object, it will be deleted
during destruction, this is the case for loaded audio files.

Also, a few ugly casts were removed.
Merge tag 'v0.26.0' into archlinux

Alpha 26.
Turret health 190 → 250, price 8 → 10. Armoury price 10 → 8.
Rework burning code. Fire spread should be a bit less aggressive.
Synchronize creep marks and creep effects (e.g. slow) via the config file "creepSize" value.
»give health <amount>« sets health to the given value.

This is my first non-C89-compatible commit to the gamelogic! Yay!
Rework alien health regeneration.

Heal rate changes:
- In the open:       1x (unchanged)
- Inside base:       2x (from 3x)
- Close to teammate: 2x (new)
- On actual creep:   4x (new)
- Close to booster:  8x (from 9x)
Remove film grain and vignette effect
Bump Debian standards version.
Initial work on implementing the filesystem in the vm
Add comparison operator to AudioData
Fix typo