invertible parsing and printing; documentation

 Specify a single unified grammar which can be used for parsing and
 pretty-printing.
 .
 Boomerang is a DSL for creating parsers and pretty-printers using a single
 specification. Instead of writing a parser, and then writing a separate
 pretty-printer, both are created at once. This saves time, and ensures that
 the parser and pretty-printer are inverses and stay in-sync with each other.
 .
 Boomerang is a generalized derivative of the Zwaluw library created by
 Sjoerd Visscher and Martijn van Steenbergen.
 .
 This package contains the documentation files.