bump 2.9.1

moved print to stderr to logger function

* monkey patching logger will replace the print to stderr functionality instead of supplement it

bump 2.9.0

bump 2.8.0

bump 2.7.0

bump 2.7.0

Merge pull request dronekit#631 from brenton311/master

Added copyright notice to example files.

Merge pull request dronekit#621 from dronekit/rroche/bump-2.5.0

bump 2.5.0

Merge pull request dronekit#587 from dronekit/tcr-please

Catch and display message and attribute errors, then continue.

Merge pull request dronekit#598 from dronekit/rroche/bump-2.4.0

bump to 2.4.0