Roughed in some forwards.
Shelled a ton of modules.
Implemented stream_i, stub stream, unit test.
Implemented file stream.
Buffer, unit tests.
Trie, trie fixture, unit tests.
Implemented button map, unit tests.
Added modules for button and text reader ifaces, forwards.
Button reader, mock handler, reader fixture, unit tests.
Modifiers, unit tests.
Moved a few input defs into input namespace.
Renamed button_t to button_id_t, updated var names.
Added individual modifiers, io, unit tests.
Added modifier collection, io, unit tests.
Correctly ordered includes in modifier-io.cpp.
Added using namespace testing to terminal-lib-test.hpp.
Events, handlers, and unit tests.

- Shelled some basic event classes and their hierarchy, simple
unit tests.
- Built event handler, unit test.
Added code point to text event.
Added stream iface, stub, file stream, unit tests.
Added buffer, unit tests.