candidate fix for get_motion_params() bug

- Change integration style.
- Update tests to accomodate integration style change.
- doc revision for get_motion_params()
Split gmpy & matplotlib tests again (to 3 splits)
Merge pull request #2545 from zanzibar7/get_motion_params_bugfix

candidate fix to get_motion_params() for issue #2543

close #2543
Merge pull request #2555 from skirpichev/travis-3

Split gmpy & matplotlib tests again (to 3 splits)