Update to Rust master

Closes #17
fail -> panic
Merge pull request #18 from zsiciarz/master

fail -> panic
Fix warning about renamed missing doc attribute.
Merge pull request #19 from jbcrail/fix-missing-doc-warning

Fix warning about renamed missing doc attribute.
bigint: Remove parse_bytes method

This follows the changes of "Separate string->integer implementation in strconv" (rust-lang/rust@138b76b)
Use sliciing_syntax
Fix lint name warning