auto merge of #5583 : jbclements/rust/docfix-for-block-comment-grammar, r=jbclements

... by adding Kleene '+' in two places, and changing a "non-slash" into "non_slash_or_star".

Closes #1588
field renaming
commenting parser
change to parsing using tts

also, updates test cases a bit
path -> Path
libsyntax comments
add MTWT functions, make idents managed
comments, cleanup
mod.rs cleanup and renaming
cleanup, renaming
syntax test cases pass
adding parse_path part 1
jbcdone tracking (should never wind up in upstream)
temp, shouldn't go upstream
adding parse_path part 2
moved tests to ast_util, changed to use idents as names
simplify, based on invariant that items_allowed != foreign_items_allowed
jbcdone, not to go upstream
using invariant again
jbcdone no upstream