cleaning up gpsdo docs
BUG 298:  B200: timed receive does not work on B210
BUG 299:  UHD: test_timed_commands divides difference by 100
Changed stream_now to false, added assignment of time_spec to command, and fixed typo.
manual: Added RF ranges of B2x0 devices
Merge remote-tracking branch; fixing timed_commands example
Updating CHANGELOG for 003.006.002
Updated UHD images URL to new release package
Added timed control commands to test_timed_commands example.  Added radio core as subscriber to tick rate change for B200.
Merge branch 'bug298'