update single-cell protocol documentation

Add inDrop v2 to alevin

Fix corner case logic bug where barcode recover attempted even if extracted_barcode was `false`.

Add sci-rna-seq3 protocol to salmon

Bring `UMIBarcodeT` back into line with what is in develop.

- add A to 20 bp cb and AC to 19 bp cb

Remove extra ":" from `salmon_version` in `cmd_info.json`

Refactoring

spacing -- re-trigger CI

* argument parsing

* allow early load of the index

- add padding with A to make bc len constant
- if w1 not found search with hamming distance 2

This addresses #688 by adding reasonably fully featured cmd_info.json
and meta_info.json files when alevin is run in RAD mode.  Some
fields are not present in meta_info.json, but important ones like
the sequence hash are.