Add export-to-wav CLI utility.

[trh-x]

export-to-wav

This PR introduces a command-line utility called export-to-wav which can be used for scripting exports.

Multi-track

The utility includes the ability to export in multi-track mode. When doing so, WAVs which are silent will automatically be removed.

Usage

Usage: ./build/src/tools/export-to-wav/export-to-wav <input.xm> <output.wav> [options]
Options:
  --sample-rate <rate>  Sample rate in Hz (default: from settings or 44100)
  --volume <volume>     Mixer volume (default: from settings or 256)
  --shift <shift>       Mixer shift (default: from settings or 1)
  --resampler <type>    Resampler type (default: from settings or 4)
  --multi-track         Export each track to a separate WAV file

When using --multi-track, output files will be named:
  output_01.wav, output_02.wav, etc.
  (Silent tracks will be automatically removed)

Notes

A few other changes are included, some of which might be preferable to omit or merge separately:

• Add trackerlib library to allow reusing code from the tracker in the CLI utility.
• Switch C++ standard to C++11 (see Switch C++ standard to C++11 #328).
• Add functionality to build.sh:
  • Allow a debug build to be built.
  • Allow DMG generation to be skipped on Mac.

[coderofsalvation]

Very cool!
Btw. have you seen: 31ba8a9

Which is basically:

I really like love the idea of having this available in a scriptable/batch way (for example to use in combination with faircamp)

questions:

1. Could this be also added to the milkytracker binary (right now it just detects one arguments, and loads it as a module).
2. should we rename trackerlib to commandlib or clilib or something to make it more specific

Reason: I've been thinking of a cli interface for milkytracker before, and I can think of more usecases (besides exporting). For example: we have some env-vars (MIDI_IN and SCALE_NEAREST) but they are very hidden in the docs.

So WDYT about this:

$ milkytracker --help
Usage: milkytracker [options]
Options:
  --export <input.xm> <output.wav> [options]  export input to WAVs
  
      --sample-rate <rate>                              Sample rate in Hz (default: from settings or 44100)
      --volume <volume>                                Mixer volume (default: from settings or 256)
      --shift <shift>                                          Mixer shift (default: from settings or 1)
      --resampler <type>                                Resampler type (default: from settings or 4)
      --multi-track                                            Export each track to a separate WAV file

       When using --multi-track, output files will be named:
       output_01.wav, output_02.wav, etc.
        (Silent tracks will be automatically removed)

Then later --midi-in and --scale-nearest can be added as args, and who knows what.