Set up testing environment
Update documentation

- Split readme.md into readme.md and details.md.
- Move all link definitions to the end.
- Recommend installing into library folder.
- Add timeline.
Fix tests: Create `Dual` instances in each test

Not in setup.ahk.
Refactor, including `new Dual({setting: value})`

Obsoletes `dual.setting := value`.
Add the `modifier()` method.

This includes being able to turn off the `timeout` and `doublePress`
by setting them to `-1`.
Release 0.4.0