add basic id/sid mapping in the Collada object; add newparam and SIDREF classes
change articulated_system to use the NewParam class
add FIXME messages for potential bugs
Collada.addSid() needs to map all the nodes from a sid
small bug fix: tag('SIDREF'), not 'SIDREF'
resolve() for NewParam and resolve() for SIDREF; these essentially work, except that url attributes are not accounted for; this is a bug that needs to be fixed
fix NewParam.resolve() to keep walking until done (i.e. until we hit a literal value)
switch the node to search from if a url attribute is present
add "abstract" getchildren() method to DaeObject, along with implementations for subclasses
add BFS for searching for a sid path
if url is present, switch the node to search from (BFS)
prismatic and revolute joints
tiny spelling typo
FIXME comment
getchildren() for kinematics_scene
getchildren() for assets
Merge branch 'add-newparam-sid-walking' into add-sid-bfs

Conflicts:
	collada/asset.py
	collada/joint.py
just a quick comment
add method to get an object directly by id (from the ids_map)
add a map -- analogous to ids_map -- for ids with suffixes, and a function to add to it