PX4-Autopilot

Release candidate with a number of improvements and bug fixes:

• Optional attitude_estimator_q from Anton Babushkin (@DrTon, lightweight, elegant, estimates gyro offsets)
• New mixer: Modifies collective throttle to keep system stable when motors saturate (by @tumbili)
• Preflight checks: Prevent takeoff with unhealthy system configurations (by @Zefz)
• Logging: Default to 100 Hz on Pixhawk (user-configurable via parameter)
• MAVLink FTP: 30x speedup and bugfixes (by @DonLakeFlyer)
• Improvements for gyro, mag and accel calibration (more rigour but also more user assistance)
• MPU6K, LSM303D and L3GD20(H): Reject duplicate measurements (by @tridge Andrew Tridgell)
• Better boot error reporting (by @sjwilks)
• Fix airspeed handling in ECL fixed wing controller (by @thomasgubler)
• Firefly Y6 support (by @tumbili)
• Only transmit used parameters feature + fixes, speeds up param transfers (by @davids5)
• Fixes for state-level HIL
• Fixes for offboard control with velocity commands
• Param meta data by @DonLakeFlyer
• STM32F4Discovery support (by @nopeppermint)
• Various mavlink fixes (by @NaterGator)

Fixed microSD on FMUv1

• This release candidate changes the default attitude and position estimator for all platforms to ekf_att_pos_estimator. From @Zefz.
• EKF offset fixes. From @sverling.
• Landing detector. From @Zefz.
• NuttX/ROS multi-platform improvements. From @thomasgubler.
• RAM optimizations. Brings FMUv1 back within limits (even when running two MAVLink links)
• Offboard / companion computer control: Support ACTUATOR_TARGET. From @matt-beall.
• Increase RTL descend altitude for fixed wing. From @AndreasAntener.
• PWM input driver. From @Slayte via @tridge.
• Oreo led and smart battery drivers. From @rmackay9.
• Initial rover support from @mstuettgen
• mkblctrl improvements from @NosDE
• Offboard control fixes by @ziyangli
• Enforce one speed per I2C bus

Complete release, including multicopter, fixed wing and VTOL support.

Complete release, including multicopter, fixed wing and VTOL support.