Support SQLite column definitions with no type

[takluyver]

SQLite allows columns with no type information:

CREATE TABLE t1 (a, b AS (a * 2), c NOT NULL)

As far as I know, other SQL databases all expect a data type for each column. So for now I've allowed this only for the SQLite dialect. Should the generic dialect also support it? The docs suggest that it's 'permissive', but I wasn't sure if this would be stretching the point too far. 🙂

Closes #743

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Change from base Build 7303175792:	0.1%
Covered Lines:	18652
Relevant Lines:	21239

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[alamb]

Thank you @takluyver -- this is looking good to me. I think @tobyhede has a good style suggestion and it would be really helpful to improve the doc comments before we merged

Should the generic dialect also support it? The docs suggest that it's 'permissive', but I wasn't sure if this would be stretching the point too far.

I don't have a strong opinion. We can maybe start with SQLite only and then expand coverage for generic dialect if people want it

[takluyver]

Thanks both! I've renamed the helper message and tried to document this feature better.

[alamb]

LGTM -- thank you very much @takluyver (and happy new year 🎉 )

[takluyver]

Thanks! Happy new year to you 🎆