Add simple linked-list iterator for TreeNodes.
Fix typo in parser.
Link symbols in the AST to their declarations.
Don't shadow func defs when calling vars with same name.
Finish documentation for declaration linking.
Type check expressions.

Represent types with new BPLTypes class.
Type check statements.
Fix return statements, array/variable/address expressions.
Finish documenting type checker.
All tests take bpl files thru command-line args.
Merge pull request #9 from daf-/type-checker

Type checker