Upgrade MSFA to incorporate Dexed improvements and fixes

[micahscopes]

changes

• Integrates MSFA code from Dexed
  • slight, inconsequential adaptations were necessary to get this working
  • temporarily disabled new MSFA microtuning features
• upgraded the build process to work with recent versions of emscripten
• streamlined build/distribution process in Makefile
  • updated relevant build docs
• clarified licensing for project and dependencies (fixes License? #7)
  • This library is MIT licensed, as clarified in License? #7
  • Dexed readme explicitly states that their MSFA changes maintain the original Apache 2.0 license, so I included original Google license doc in the MSFA source directory
  • New tuning-library dependency is permissively licensed (I think using MIT license)

context

I've been using webdx7 in a project and noticed that some of my presets weren't rendering correctly (compared to Dexed).

On investigation, I figured out that the Dexed contributors have made a number of improvements to the MSFA code, including tuning and additional implementation of DX7 features. My specific issues seemed to have to do with a previously unfinished LFO implementation.