Merge pull request #206 from Craig3DRobotics/master

Changed Instructions for uploading firmware to PX4
AP_Param: fixed assignment handling and const

this fixes radio_min = radio_max = radio_trim = 0; in RC_Channel
AP_Param: added ops needed for ArduCopter build
AC_WPNav: improved comments

Made SPEEDZ a parameter although it's not yet used
AC_WPNav: add climb and descent params, dynamic leash length
Copter: auto climb and descent params removed

These params now reside in the AC_WPNav library
Copter: remove unused AUTO_VELZ defaults

These have now moved to AC_WPNav
Copter: add WP_YAW_BEHAVE parameter

Allows user to control whether nose points towards next waypoint and/or
home when RTLing.
Replaces YAW_OVR_BEHAVE which had a very similar purpose.  Almost nobody
ever knew about or used this parameter.
Copter: bug fix for take-off so it never descends

If copter was already flying when take-off command was received it could
descend to the target altitude if it was below the current altitude.
AutoTest: reduce throttle so it doesn't fly so far
AC_WPNav: remove unnecessary limit in leash calc
AC_WPNav: increase max descent speed to 1.5m/s
Rover: fixed dataflash logs to be useful

added sonar and fixed other messages
Plane: added gps status to flashlog
autotest: fix dump_logs for other vehicle types
autotest: added command line extensions to sim_rover.sh
Rover: fixed turn time in flash logs
Copter: make CIRCLE_RATE a tunable parameter

Also bug fix to check of how many time it has rotated during a loiter
turns mission command
AP_AHRS: made a few methods const
AP_Param: make it easier to show the value of a parameter