Add utilities to compute identifiable parameters of an msspoly expression
Add multi-column decimate function to utils
Replace `decimateMultiCol` based on MATLAB built-in with naive loop-over-columns implementation.
Fix frame handling in `findFixedPoint`.

`findFixedPoint` (both in `RigidBodyManipulator` and
`TimeSteppingRigidBodyManipulator`) now outputs a `Point` in the state
frame.
Merge branches 'tsmanip-frames' and 'multi-column-decimate' into parameter-estimation
Breaks parameterEstimation into smaller pieces for easier debugging
Let parameters be set with msspoly values
Trying out streamlined dynamics/statics functions
Add s^2+c^2 = 1 simplification to cleanIfNecessary in G.m
Fix typo in `baseParameters.m`
Fix handling of params in `removeFixedJoints`.

Now, if the parent or child link of a fixed joint has parameterized
inertia, mass, or com properties, `removeFixedJoints` will attempt to
parameterized the corresponding properties of the combined link. This
can fail fairly easily when updating the com, as, for links with
non-zero mass, this requires dividing by the sum of the link masses.
Despite this limitations, the current implementation is quite useful in
that it allows for the construction of `PlanarRigidBodyManipulator`
objects whose floating-base links have inertial parameters.
Add exploration script for Atlas parameter ID
Standize joint names and add `origin` tags to `simple_quarter_atlas` and `qatlas`
Add `simple_quarter_atlas_param.urdf` with inertial parameters.
Clean up Atlas parameter id. exploration script
Add script to proccess qatlas static data.
Fix frames in explore script. Runs well.
Add xslt stylesheet that adds inertial params.

Tested with saxonb-xslt. Usage:

$ saxonb-xslt -s:<source-urdf> -xsl:parameterizeInertialElements.xsl \
> -o:<output-urdf>
Add planar quarter atlas model.
Switch explore script to use planar model.