Use list of lists to construct Records in dshape

[mrocklin]

We should support construction of all datashapes through python syntax and data structures. This allows for simpler programmatic construction than string manipulation.

One case where this is difficult is records, e.g.

'{name: string, amount: int}'

In datashape the order matters while in Python the order doesn't

{'name': string, 'amount': int} == {'amount': int, 'name': string}

The standard fallback is to use a sequence of items

[['name', string], ['amount', 'int']]

Maybe the utility function dshape should recognize this situation and produce the appropriate Record

[cpcloud]

closing in favor of #71