v0.10.0

This is a big release as we're moving to rust 2018 edition!

New

• More badges in the readme.

Changed

• Use rust 2018 edition.
• Minimum rust version is 1.38.0
• Update arcswap, serde-value and serde-xml-rs.

Fixed

• Deprecate len method on rolling_file.
• Windows build issue after 2018 edition.