Add some functions for Bytes

[traceflight]

Hi @udoprog, this pr updates some functions of Bytes.

1. Adds push, remove, insert, index_get, index_set functions.
2. Registers first function, it seems that it was forgotten to be registered.

[udoprog]

Hi and thanks!

The error is just a line ending at the end of the script, you can format them the way Rune wants it like this:

cargo run --bin rune -- fmt --verbose --recursive scripts

[udoprog]

Thank you!