This patch introduces Browser Contexts and methods to manage them:
- `browser.createIncognitoBrowserContext()` - to create new incognito
context
- `browser.browserContext()` - to get all existing contexts
- `browserContext.dispose()` - to dispose incognito context.
Fixes#85.
This patch introduces a new `pipe` option to the launcher to connect over a pipe.
In certain environments, exposing web socket for remote debugging is a security risk.
Pipe connection eliminates this risk.
