Implement a function to splice parsed-program objects together in a reasonable way.

It looks like the upcoming sbcl 2.0.1 release includes changes to move certain symbols out of cl:*features* and into sb-impl:+internal-features+ [[1]]. IIUC, any "non-public" features will continue to work (for now), but issue a warning [[2]].

I haven't tested it, but it looks like we use at least one such soon-to-be-deprecated feature, namely avx2. We should figure out what to do about

All other documentation source files are only rst or ipynb.
superoperator_representations.md should probably be removed.

EDIT: It looks like some of the material was imperfectly translated from markdown to rst. So there is reason to keep both for the time being.

The ls and resolve commands shows my .pinset entry as having a size of 60. Let's force it to add units in all cases.

? > ls
.       2.4G  QmSc9pcnm4N1QC1u2oSNL6eRgFjxDq2Aex6cGhTkvw91xc
.pinset 60    QmYJmoKWDFh1wmZLATh3fiVzMuhhTyNm9NLGuLEJM7HdNZ
dapps   17.5M QmQN6bA5YEPEaPDUDLq6o9fm24Ye2bbnA4YUT2rBeAR5cm
foo     2.4G  QmPkNdFzNFZfM9QixL3ZowBNvveFmufbnRuM36K1SrnmB1