Batch indexing (multiple inserts)

[leodido]

Support SphinxQL multiple row insertion.

The INSERT syntax to achieve this task is explained by following example:

INSERT INTO rt_index [(col_a, col_b)] VALUES
    (val_a1, val_b1),
    (val_a2, val_b2)
    [, (...)]

Documentation says that

Multiple rows can be inserted using a single INSERT statement by providing several comma-separated, parentheses-enclosed lists of rows values.

This behaviour is available also for REPLACE statement.

Reference here.

[leogr]

zendframework/zendframework#4028

I think it's specific of some SQL dialect so it makes sense to implement this functionality in our library.
I'll do that.

[leodido]

This is not the only way to index multiple documents at once but it is the most efficient.
Reference here, 2nd part.

👍