BudCollection#schema is confusing

[jhellerstein]

It is handy in a state block to reuse the schema of a previously-defined collection, but using BudCollection#schema does not preserve the key dependencies. E.g.:

  state do
    table :orig, [:kee] => [:wal]
    table :oops, orig.schema
    table :yeps, orig.key_cols => orig.val_cols
  end

The table oops has key [:kee, :wal], rather than [:kee]. But the table yeps is annoying to type, so it's easy to introduce bugs by doing what oops does.

[neilconway]

Yep, this is definitely confusing. How about:

1. Change BudCollection#schema to return key => vals (input schema)
2. Add BudCollection#cols to return the list of column names in the collection's schema. This is nicely symmetric with the existing key_cols and val_cols methods.

[jhellerstein]

concur on the proposed solution.

[neilconway]

Okay -- I can take a crack at implementing it.

[michaelficarra]

I opened pull request #247, which should mostly take care of this issue.

[neilconway]

Merged #247 with additional fixes -- this should be fixed.