This allows one to obtain the length of a fixed-length vector that has--for
example--been cast to a different datatype, squared, etc.

Fix 215

BatchedDot only supports tensor3

fixing broadcasting behavior in BatchedDot

adding test for TypeError on dimension mismatch

removing extra tests

Get rid of singleton design and most module-level variables

Provide pointer to working docs.

Update print warnings to use warnings.warn

Refactor config code

This commit also removes redundant "WARNING" and "DEPRECATION" strings and, for
the latter, sets the category (or raises) a `DeprecationWarning`.

This makes them easier to refactor and easier to invoke from elsewhere.

The hierarchical config settings are hard to maintain and hard to debug. Now
sections are marked by dunders. This is the way!