Added header file with common physical constants.
Updated library functions to use physical constants file.
Updated flight modules to use physical constants file.
Updated PiOS files to use physical constants file.
Updated GCS files to use physical constants file.
Added the shared API directory to simulator targets.
Fixes for header files, floating point trig functions, and incorrect
conversions.
Added shared/api to GCS include directory.
Fixed missing newline.
UAVTalk: Fix crash when requesting update of unknown object

UAVTalk would check whether an unknown object was single instance
even if the object type was unknown, which caused a segfault.  This
value is only used to validate the payload length (possibly an
unnecessary check) so now that check is not applied if the object
is unknown.

The response to an OBJ_REQ for an unknown object is simply to return
a NAK packet so this should keep multiple instance objects ACK'ing
properly while solving the segfault for unknown objects.

Any non OBJ_REQ message should not even reach this far as they should
error our with a bad object type.

Fixes #80
Fixes #358
Resolved merge conflict.
Merge pull request #328 from kubark42/phys-constants

Group all physical constants into one file
Fix copyright
UAVTalk: Refactor some logic.  No functional changes.
Merge pull request #400 from peabody124/uavtalk_80

UAVTalk: Fix crash when requesting update of unknown object