Don't generate glob imports in grammars

Glob imports require the user to use #[features(globs)], so let's not
generate them if we don't need to.
Allow \u{...} to be used in grammars

Note that this only handles the input side, not the output side.  Fixing
the output side will require changes to libsyntax.  Support for old
style \u and \U escapes has been left in for now to ease the transition.
Merge pull request #34 from emk/new_unicode_escapes

New unicode escapes
test_arithmetic.rs: Update for latest nightly
rust: rebuild grammar.rs for unicode syntax pprint change
rust RFC#378: Trailing semicolon on item macros in test_arithmetic
rust: API deprecations
Update readme with docs on using as a syntax extension and Cargo.
0.1.2