REPL - Enhancements

[brekk]

Some initial feedback / requests on the current state of the REPL, which came out in 0.20.0 — these are all ideation and aren't necessarily something we've committed to yet:

• - Home / End / Cmd+Right / Cmd+Left to move the cursor
• - :multi + up-arrow is subpar UX, maybe we could either inline the previous statement or jump back into multi mode or something (not certain here, but weird to hit up-arrow and see . as the previous command
• - Not sure the proper name, but something like :context or :scope to print all the variables which are currently resolvable in the sandbox
• - Some kind of :export tooling, which combined with :context would allow you to select values to export from the sandbox to a standalone file
• - This goes more towards snang but possibly some tooling to afford IO + standalone repeatable runs (likely afforded by :context + :export