[WIP] An initial program printer

[jmid]

This PR takes a stab at adding a program printer #56.

This first version

• prints a corresponding program without performing a sequential consistency search
• only supports Domain currently

It can be enabled by setting an environment variable as follows:

LIN_PRINT=1 dune exec src/hashtbl/lin_tests_dsl.exe

When set,

• /tmp/linfail.ml will get a print of the last failing cmd triple
• /tmp/linlast.ml will get a print of the last tested cmd triple

(both of these will currently over-write)