This patch:
- adds `page.touchscreen` namespace, similar to `page.mouse` and `page.keyboard`.
- adds tapping to multiple layers:
- `page.touchscreen.tap`
- `page.tap` - convenience method which accepts selector
- `elementHandle.tap`
Fixes#568 and #569.
This patch:
- adds Mouse class which holds mouse state and implements mouse primitives,
such as moving, button down and button up.
- implements high-level mouse api, such as `page.click` and `page.hover`.
References #40, References #89
This patch implements Basic Input api:
- Page.focus(selector) - focuses element with selector
- Page.click(selector) - clicks element with selector
- Page.type(text) - types text into a focused element
Fixed#43.
