Fix panics with whitespace in extended mode by being more strict
Fix panics with whitespace in extended mode by being more strict

Instead of ignoring space in all the bump/peek methods (as proposed in
pull request #349), have an explicit `ignore_space` method that can be
used in places where space/comments should be allowed.

This makes parsing a bit stricter than before as well.

rust-lang/regex,rust-lang-nursery/regex,rust-lang/regex,rust-lang/regex,rust-lang-nursery/regex,rust-lang-nursery/regex,rust-lang/regex,rust-lang-nursery/regex,rust-lang-nursery/regex,rust-lang/regex