update changelog
"0.5.6"
Ported tutorial from wiki to sphinx in source repo.
Merge pull request #67 from ros-planning/setup-assistant-tutorial-sphinx

Ported tutorial from wiki to sphinx in source repo.
Added back-link to tutorial and updated moveit website URL.
Merge pull request #68 from ros-planning/back-link-and-url

Added back-link to tutorial and updated moveit website URL.
Update for 0.5.7
"0.5.7"
Fix for issue #70: support yaml-cpp 0.5+ (new api).
Fix for yaml-cpp 0.5 (break for yaml-cpp 0.3).