Primary API for HoneySQL 2.x.

This includes the `format` function -- the primary entry point -- as well
as several public formatters that are intended to help users extend the
supported syntax.

In addition, functions to extend HoneySQL are also provided here:
* `clause-order` -- returns the current clause priority ordering;
      intended as aid when registering new clauses.
* `format-dsl` -- intended to format SQL statements; returns a vector
      containing a SQL string followed by parameter values.
* `format-entity` -- intended to format SQL entities; returns a string
      representing the SQL entity.
* `format-expr` -- intended to format SQL expressions; returns a vector
      containing a SQL string followed by parameter values.
* `format-expr-list` -- intended to format a list of SQL expressions;
      returns a pair comprising: a sequence of SQL expressions (to be
      join with a delimiter) and a sequence of parameter values.
* `register-clause!` -- register a new statement/clause formatter.
* `register-fn!` -- register a new function call (or special syntax)
      formatter.
* `register-op!` -- register a new operator formatter.
* `set-dialect!` -- set the default dialect to be used for formatting.
* `sql-kw` -- turns a Clojure keyword (or symbol) into SQL code (makes
      it uppercase and replaces - with space). 

Helper functions for the built-in clauses in honey.sql.