Add musical optimization examples and modernize C++ code

[thorinside]

This commit adds three new musical applications that demonstrate how
to use the NGAL genetic algorithm library for audio synthesis and
music parameter optimization:

1. synth_optimizer.cc - Waveform synthesis parameter optimizer

   • Finds optimal harmonic amplitudes to approximate target waveforms
   • Demonstrates additive synthesis parameter discovery
   • Example: synthesizing sawtooth waves from harmonics

2. oscillator_params.cc - Oscillator parameter optimizer

   • Finds musically interesting synthesizer parameter combinations
   • Optimizes 6 parameters: frequency, FM depth/ratio, wave shaping,
     filter cutoff, and resonance
   • Balances spectral richness with musicality

3. rhythm_evolution.cc - Rhythm pattern evolution

   • Evolves musically interesting 16-step rhythm patterns
   • Optimizes for syncopation, density, and dynamic range
   • Creates patterns with velocity and articulation information

Also includes:

• MUSICAL_APPLICATIONS.md - Comprehensive guide for musical applications
• Updated Makefile to build new examples
• Modernized C++ code to work with current compilers
  • Replaced deprecated _G_uint32_t with standard uint32_t
  • Replaced deprecated _G_config.h with stdint.h
  • Fixed compatibility issues with modern glibc

These examples demonstrate practical applications of genetic algorithms
for musical parameter optimization, sound design, and pattern generation.