spreadsheet v0.1

Functor for parsing and building spreadsheets.

Defines a spreadsheet functor and RowSpec module type.
When given a RowSpec, the functor produces a module that will represent a
spreadsheet backed by a set.
The programmer must provide a RowSpec module, which is essentially:

• An OCaml type to describe spreadsheet rows.
• Coercions from the row type to/from string.
• A string list title describing each column of the spreadsheet.