Check support for named fields in update/upsert

[nicktorwald]

Add required tests that show support for named fields introduced in
Tarantool 2.3. This feature affects update and upsert operation
triplets allowing to use field names specified as a space format.

Extend operation DSL part to use named field in addition to numeric
ones.

Closes: #220

[coveralls]

Coverage increased (+0.05%) to 77.686% when pulling 5fa568c on nicktorwald/gh-220-update-by-field-name into f32bafa on master.

[Totktonada]

Answered questions in cc8d73a comments. In short, those operations are possible when we're working with nullable fields.

As far as I see named fields works properly with (client ops).update() API? So we need to just add tests on them to close the issue? If so, we can merge those tests separately if you'll open a separate PR about that.

We have Lua style guide: it would be good to follow it in examples. I mean, { foo='bar' } should be {foo = 'bar'} — whitespaces around =, but not after { and before }.

[nicktorwald]

Thank you for the answers. Now it is clear. I extended the test cases where I Included two more operation types mentioned above. Also, I removed extra whitespaces to follow the style guide. Hope, after schema update is merged It will be a good candidate to be released next.

[Totktonada]

The new tests against ops.{update,upsert}() looks good for me, other parts of the PR are subjects to extract into PR #247.

[Totktonada]

LGTM.