Sql: extend supported syntax

Here are some related POC proposals for extending the syntax supported by the Sql class to improve it as a standalone query builder. I'll leave these as separate commits for your convenience:

- [x] Replace named params with positional params to allow repeat references, resolves #30
- [x] Add ability to use open/close brackets in any part of a statement for grouping and nesting
- [x] Add support for merging nested subqueries
- [x] Allow raw queries to be set or appended with passed parameters and subqueries
- [x] Allow query reuse for logging, profiling, etc.
- [x] Add shortcuts for aliasing subqueries and columns.