simplify, based on invariant that items_allowed != foreign_items_allowed
remove unnecessary function
reindent in parser
get rid of prec.rs

prec.rs no longer had much to do with precedence; the token->binop
function fits better in token.rs, and the one-liner defining the
precedence of 'as' can go next to the other precedence stuff in
ast_util.rs
comments
top-of-file comment for syntax.rc
parser comments
refactoring
refactoring to split foreign_items from items
continued refactoring
removed old type dispatch test
parser refactor to separate foreign items
continued refactor
dead code check
refactor more
parser comments
parser refactor cleanup
parser comments
reorder clauses in item parser
rename parse_non_foreign_item_or_view_item to parse_item_or_view_item