Made download_rtsp method non-blocking by default

Updated README based on API changes

Update requests are now throttled to prevent unintentional hammering …

…of Logi API.

Added methods and properties for setting and monitoring the camera’s …

…battery saving mode.

Added @requires_ffmpeg decorator to prevent ffmpeg dependent function…

…s from being executed if ffmpeg is not installed.

Other improvements:
- subprocess calls no longer requires shell and now correctly handle paths with spaces.
- record_livestream now truncates the output file to precisely match the requested duration.
- Comment style clean-up.

Fixed missing `last_activity_time` sensor on 2nd gen wired cameras.

Renamed `model_name` to `model_type`, added model type based feature …

…detection to simplify HASS integration.

Bumped version to 0.1.2

Improved live stream support, added lots of new camera properties and…

… methods

* Live streams now download at real-time speeds (assuming no connection bottleneck)
* Live streams will append to an existing file by default (instead of overwriting)
* Lots of new camera properties and methods, see README.md for more detail.