To Do List for SQL::QueryBuilder::Simple

General features to add:
  - more comprehensive testing.
  - possibly embedded tests (using Pod::Texts).
  - implement a disabled use_bindings()
  - implement a pretty() flag that enables "pretty" SQL output

SQL Features to add:
  - support for simple aggregate functions, GROUP BY.
  - support for additional clauses (BETWEEN)
  - support for comparing fields (WHERE FLD1=FLD2).