put flight tasks in separate folder and create a lib for each
goal is to select tasks for targets (e.g. because of flash issue)

The default is auto-detect, but some GPS devices might not like that, such
as the Trimble MB-Two.

Otherwise the conversion from mavlink_mission_item to mission_item
will cause the latitude and longitude of the ROI to be off by a factor of 1e7
in the case of INT mode.

_subscriptions is a vector that is resized when needed. However there could
still be references to elements in the vector when the resize happens.
These references then become invalid.
Using a vector of pointers fixes that.

px4iofirmware: moved the simple register updates down to the fall-through block, moved the sbus rate update up so it doesn't get called on each of the other updates which would set the wrong value

mixer: set/get_trim needs to return the amount of channels consumed by the mixer even if the mixer doesn't support trims (or is empty)

Add doxy styling to method comments and update comments, replace goto statements with stop() calls and return statements.

 - the valid values are 0-999999

    - micro-CDR in PX4/Firmware (1332d4dbc224a2980c37572be951d247a5698b9b): https://github.com/eProsima/micro-CDR/commit/92efe34b65622aef3d41315230cec0bce37a27e3
    - micro-CDR current upstream: https://github.com/eProsima/micro-CDR/commit/8125eac84c11d70ce148da4b67b2d73d46bf6c33
    - Changes: https://github.com/eProsima/micro-CDR/compare/92efe34b65622aef3d41315230cec0bce37a27e3...8125eac84c11d70ce148da4b67b2d73d46bf6c33

    8125eac 2018-08-03 Ricardo González Moreno - Merge commit 'c571c7f22602d88d2415ea46c19fb5d81e0260f1' into hotfix/enable_language
c571c7f 2018-08-03 Ricardo González Moreno - Squashed 'cmake/common/' changes from a4f9b91..9e7f35b
99cb75d 2018-08-02 Ricardo González Moreno - Hardening the warnings.
775a847 2018-08-02 Ricardo González Moreno - Removed warnings in windows.
cd13d68 2018-08-01 Ricardo González Moreno - Changing jenkins support to toolset.
6f2c623 2018-07-31 Ricardo González Moreno - Added files to support jenkins.

- v2.0 in PX4/Firmware (ca3e4a53): https://github.com/mavlink/c_library_v2/commit/2c4b0e9ff26ce4900a72335912e2604a1e9948de
    - v2.0 current upstream: https://github.com/mavlink/c_library_v2/commit/6404047979cadac62fecd75070cd995f1ca66ca2
    - Changes: https://github.com/mavlink/c_library_v2/compare/2c4b0e9ff26ce4900a72335912e2604a1e9948de...6404047979cadac62fecd75070cd995f1ca66ca2

6404047 2018-08-03 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/b4871443354d607298b6f67bedd6c473c69c659a
d0fb5b8 2018-08-03 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/1ba233efffb54a7ed634160cd11855b3f5021b74