* See

https://groups.google.com/d/msg/sqlparse/huz9lKXt0Lc/11ybIKPJWbUJ

for some interesting hints and suggestions.

* Provide a function to replace tokens. See this thread: https://groups.google.com/d/msg/sqlparse/5xmBL2UKqX4/ZX9z_peve-AJ

* Document filter stack and processing phases.