Switch to standalone version.

This is prototype aiming at solving ticket #2.

Remaining issues are the dependencies w.r.t resource_retriever and
roscpp. They both can be removed if we accept losing some features.
add package.xml to keep ros
Update contact information
Merge pull request #3 from aclodic/standalone

Almost standalone version
Add urdfdom_headers needed by tests/
Merge pull request #7 from aclodic/standalone

Add urdfdom_headers needed by tests/
workin version
Allow customization of special joints names (Revisited by Florent Lamiraux)
Add missing dependency to roscpp.