Rip out debt-token related code.
ripped out more occurrences of debt token work.
Switched Matrix API to use split Shape = Frame*Grain rather than Shape*Grain for input.
Hacking in ways to specify the leaf element type in Matrix.
Add intrinsics for "true instanceof" on ParallelArray/ParallelMatrix.
This is for error checking.

Changed some of the error checking to include more information in the
error messages.

Enabled use of buffer_maker to create TypedArray backed storage when
indicated by the user.
Added toString method to ParallelMatrix just so I can see 2d visualizations.

(In particular, unlike ParallelArray.toString, the toString method
here has absolutely nothing to do with Array's toString.)