all indexing is parsed as a "container lookup"

working on robust parsing of expressions (not too easy).

also not compiling symtable.c since it's not yet being
used and generates compiler warnings.
fixing expression/assignment parsing

Golang's language spec helped a lot.
Still need to handle operator precedence using Shunting Yard
algorithm and parse 'selectors'.
selectors and function types/literals are now parsed

the function parsing contains lots of duplicated code that I plan
to eliminate in a cleanup phase.
structs and interfaces are now parsed

the AST debug output looks a little weird so they may not be
parsed completely properly but things are looking good.