v3.0.0-alpha: Add webview component

This alpha release has an enormous number of changes compared to the 2.0.0-alpha.

• Add ctl component (a utility to control the webview)
• New command: idle_time
• New event: user_activity
• Support for single-shot commands
• Add option to set a startup script on webview

v2.0.0-alpha: Merge pull request #4 from gustavosbarreto/singleshotcmd

This release contains significant changes to the last release.

Some major changes:

• Single-shot commands.
• Some fixes in response logic.
• WebSocket support.
• Screenshot command.