feat(developer): groundwork - kmx file structures

Defines kmx binary structures and wireframe builder to emit a .kmx file.

Currently the builder will emit a roughly correct header. Next steps are
to build a .kmx file with stores, groups and keys, to match existing KMX
compiler behaviour. Once that is done, will return to generation of
KMXPlus data structures.

Compiler is designed to work independent of file system so it should run
inside browser or node environment. kmldmlc.ts is node-specific, but all
other modules should be multi-platform.