Bump version to 0.20.0

Update README.md

Do not steal arguments from the script

If run as e.g. "rust-script <script> <arg>", the <arg> should always
be passed to the script, and not be interpreted by rust-script itself.

This allows e.g. a script to handle "--help" and resolves fornwall#40.

Fix clap argument handling

Bump version to 0.16 and cargo update

Bump version in Cargo.lock

Install stable toolchain for windows

Fix clippy warnings

Merge pull request fornwall#15 from fornwall/pub-fn-main

Pub fn main

Bump version from 0.10.0 to 0.11.0