Release v2.8.0

[v2.8.0]
rq: jump in version number to synchronize with robotpkg version

• Reduce the FeetConstraintXY for HRP4 and Romeo.
• Merge pull request #6 from gergondet/fixDefaultSelectorConstructor
• Fix Selector(name) constructor
• Merge pull request #5 from gergondet/topic/fixWalkingPy
• Fix some parameters in walking.py for real walking
• [travis] Add dependency in jrl-walkgen.
• Remove merge traces in the walk_romeo python script.