Generating a parser starts with creating a bnf file.
We have created an example.bnf file to illustrate this.
Running gen.sh will generate the parser, scanner and token code
needed to parse the language.

The ast (abstract syntax tree) package needs to created by the user.
This package should contain the corresponding function calls
required by the syntax directed translation rules.
See the example/ast package we have created.

Parsing a string with the generated code and evaluating the ast is
shown in example/example_test.go with some corresponding tests.
