Support bone parenting, improved merge
If the exported object parent is a bone, skin the mesh to the bone with
a 100% weight. (for big meshes it's better to do it without skinning)
When merging more objects avoid decomposing armature and animations
one time per object.
Moved the cobject transforms checks to the armature decompose and limit
them to the exported object (not to all the armature children).
Should: fix #2, fix #8.
Added only deform bones, only visible bones options
With these options bones without Deform or bones not visible are
not exported in skeleton and animations. Also all their children
are not exported (must preserve bones hierarchy).
Added some options relations.
Set more reasonable default values.
When merging the current object must be a mesh to use its name.
Review morph vertex comparison, now it compares only elements (pos,
normal, UV) which are not None.
Added more severe rules on writing file array values.
For morphs only write position, normal and tangent, not UV.
Corrected bug on morph tangent function parameter, and bug on writing
morph tangent, file were corrupted by the extra float of tangent.w.
Fix #4, fix #9