Required options:
mesh: name of mesh object(s) to add/get shapekeys to/from
(if multiple objects, make a comma-separated list)
Optional options:
loc_<x/y/z>: name of the shape key to tie to translation of the bone
loc_<x/y/z>_fac: default multiplier of the bone influence on the shape key
rot_<x/y/z>: name of the shape key to tie to rotation of the bone
rot_<x/y/z>_fac: default multiplier of the bone influence on the shape key
scale_<x/y/z>: name of the shape key to tie to scale of the bone
scale_<x/y/z>_fac: default multiplier of the bone influence on the shape key
