Materialize SQL parser

This parser is a fork of https://github.com/andygrove/sqlparser-rs, with some additional patches from http://github.com/nickolay/sqlparser-rs.

We decided to jettison compatibility with upstream so that we can perform large-scale refactors and rip out code for supporting other dialects, like MySQL and MSSQL, in favor of parsing just Materialize's SQL dialect.