Individual readability options

[HalosGhost]

A lot more encodings are now recognized and pretty-printed. This is lovely and makes the experience of poking around with lci dramatically more pleasant. However, there are times when someone may want to inspect the encoding of a particular type (i.e., view the non-pretty-printed version) without losing all the other pretty-printings. The most obvious example may be the want to keep pretty-printing lists and pairs while disabling the pretty printing of naturals, etc.

The simplest choice here would be to replace readable with an option for each recognized encoding at the moment. That is doable but tedious (no simple way to turn all of them on or off at once then). But, perhaps we could extend the option's capability to take a more interesting argument (e.g., a comma-separated list of encodings to pretty-print).

More thoughts to come.