[fidl] Remove stale TODOs from the README.md

Change-Id: I73472d86e2f39a0ada78bbd1104c60bdcd69a9b5

[fidl] Start to C header emission

This also moves ownership of library-shared resources into the
library. This includes data structures for tracking source information
and for name resolution.

Change-Id: I13c205dae445d0253d5ec84ae1ed580c42312300

[fidl] Rename 'module' to 'library'

Module and package are both rather reminiscent of particular language
notions, which we want to distance fidl a bit away from. Module,
additionally, is easily confused with modular/mods. `Library` seems to
dodge these issues.

Change-Id: I821d735e1212ecd9ffdf0a65edbcbe8796846395

[fidl] Add fidl host tool

This is the start of the fidl compiler. It parses fidl
files. Eventually this will be used directly to produce C fidl
bindings, and to emit an AST serialized to JSON for other language
bindings to consume. The first is just started in this CL.

Change-Id: I26b5e3af3e816fff17cba09417bb61c126f38f0a