Better on-disk representations

[mzabani]

• Column order no longer in each column's rep file, but rather in the table's objrep. This makes it much easier to review PRs which change column order by e.g. rewriting a table. Effects on intentional merge conflicts still unknown, but this is a secondary concern
• Full function definitions instead of a md5 hash of them. This should also make it easier to review PRs that make changes to existing functions.
• Pretty print constraint definitions
• Pretty print column types

TODO:
Modify the README to show that diffs would help review PRs changing function defnitions