support renaming columns in a table

[riastradh-probcomp]

[raxraxraxraxrax]

sqlite doesn't support this natively, so we'd have to either implement it (or work around it with ALTER TABLE, CREATE, copy, &c.)

[riastradh-probcomp]

Correct. I intended to implement this on top of sqlite3, via renaming in the compiler, and got partway through that. However, it is blocked on #38.

[riastradh-probcomp]

And by 'on top of', I meant 'outside'.