AutoPilot Improvements, Disconnect Detection

Several fixes to XY auto-flight and new funcs IsAutoTurning() and IsAutoXY() for better status reporting in apps using this package.

Also, if we don't receive a light strength update for 5s from the drone, we assume we have lost contact and explicitly close the connection.

Improve picture saving

This release addresses Issue #10 with a simple fix suggested by @Anty0 - thanks!

Picture saving is now far more reliable.

Motor start from joysticks

Besides some minor documentation changes this release fixes the joystick mapping function so that the full range of values is now sent to the Tello.

This means it is now possible to use the 'engine start' function via joysticks in the lower-inward position for more controlled takeoffs.

Fully in-and-down joysticks now cause the Tello to start the motors.

Improve Robustness, some API changes

This release adds a new function StopStickListener() which should be used when restarting/reconnecting to the drone.

The old StartVideo() function has been renamed to the more correct GetVideoSpsPps() as it actually requests SPS & PPS frames in the video stream. It should probably be called every 0.5 ~ 2.0 seconds for a smooth stream.

MVO position data is now only stored if all three (X, Y & Z) valid flags are OK - this seems to result in much better track fidelity.

There were a couple of minor changes to avoid potential race conditions.

API Changes

• StopStickListener() has been added - as above
• StartVideo() becomes GetVideoSpsPps() - as above
• FlightData.OverTemp becomes FlightData.ErrorState as the flag seems to appear on other error conditions

The last two API changes may require updates in your code

Bugfixes to improve robustness of reconnections

Two fixes to make connecting/disconnecting/reconnecting multiple times more reliable.
Also, SaveAllPics() now actually returns an error if it cannot write out the photo files.

Bugfix for potential race during control connection

Minor doc updates and a fix for a missing mutex that could potentially cause a data race during drone connection.

The fix addresses a demonstrated error shown up by the Go race detector.

Please update immediately.

Bugfix to allow repeated connection attempts

Fixes to ControlConnect() (used by ControlConnectDefault()) so that retries may be attempted after an initial connection failure.

Fixes Issue #4

Fix MVO PositionX/Y, add AutoFlyToXY()

Add AutoFlyToXY() autopilot func and various supporting funcs.
Swap MVO PositionX and PositionY over.

New and renamed automatic flight funcs

Added AutoTurnByDeg()

4 funcs were renamed:

• FlyToHeight() => AutoFlyToHeight()
• CancelFlyToHeight() => CancelAutoFlyToHeight()
• FlyToYaw() => AutoTurnToYaw()
• CancelFlyToYaw() => CancelAutoTurn() - This also cancels AutoTurnByDeg()

FlyToHeight(), FlyToYaw() and bug fixes

Started on some primitive 'autopilot' functions: FlyToHeight() and FlyToYaw()

N.B. FlyToHeight() target is expressed in decimetres.

Fixed some bugs in the flight log parsing.

Docs updated.