Refactor clause, statement and parameters storage and retrieval

[cbornhoft]

Currently each part of a query is stored in arrays. While efficient, it makes it very difficult to track where each part of a clause should go where, and if the need arises, shift parts up or down.

Each clause should have its own class, with methods specific to its clause type. There should then be a matching statement and parameter class as well.

[cbornhoft]

Updated to 3.0 release, after looking into this further, it essentially requires a full rewrite.