CmdMessenger v5.0.0

Major release:
- Python and TypeScript host clients (first-class, not just C#)
- C# async core: Task-based SendCommandAsync, TCS ACK wait, no busy-spin
- C# modernisation: netstandard2.0, SynchronizationContext, SDK-style projects
- ScottPlot 5 replaces ZedGraph in charting samples
- 247 C# unit tests (was 98), 81 TypeScript tests, 1592 Python tests
- Bug fixes: #22 (command dropping), #29 (dispose race), #31 (Digispark compile)
- See README.md changelog for full details

Update LICENSE.md

Update .travis.yml

- Updated documentation