LexState now derives copy because otherwise it is moved out of Lexer in the next! macro
PredBuilder.op is now cloned when building a Predicate
The is_* (e.g. is_exact) functions now borrow self rather than moving/copying it
ReqParseError now derives Copy to silence a compiler warning
Now clone the option inside if there is Some(x) rather than the entire option
Merge pull request #21 from burtonageo/master

Fix #20 (Compile errors with latest rustc)