documentation!

[mapsam]

Documenting this whole thing is going to be epic. A very general, evolving list of things to keep in mind (please edit inline!):

• [ ] All purpose API docs - for now we are not thinking about inline documentation (i.e. documentationjs).
  • [ ] API.md
  • [ ] C++ examples
  • [ ] JS examples
• [ ] installation, os & compiler requirements #48
• [ ] README.md - wat even is this thing #4
• [ ] CONTRIBUTING.md #10
• [ ] developer docs around algorithm choices, code structure, tests, etc. - possibly in a separate repo?

cc @springmeyer @mourner @tcql @flippmoke @jakepruitt @GretaCB @ericfischer