Split out the meaty parts of MongoCollection::insert into a C function.
Refactor so that we pass in the zval version of the collection, and not mongo_collection.

This is not really needed for the command variant, but, now it is atleast
consistent with the legacy variant.
PHP-1245: Refactor out MONGO_METHOD call for index creation.
PHP-1245: Refactor out MONGO_METHOD call in MongoCollection::save().
Put the return_value argument at the end to be consistent.
Rename arguments to be both more consistent and descriptive.
Changed "z" to "a" in MongoCollection::insert().
Merged pull request #783