Fold the evaluate CLI tool back into xpath
Remove `Clone` from inner objects
Favor String::from_str over to_string

`to_string` uses the formatting functionality used by Show, which is
overly expensive.

On a 100MB XML file, this reduced time to open, parse, and output it
to /dev/null by 1.2 seconds (taking 87% of the previous time).
Use a byte-oriented buffer instead of line-oriented

We don't care about interacting with the user here, so lines are an
artifical construct. Instead, just buffer it like anything else.

On a 100MB XML file, this reduced time to open, parse, and output it
to /dev/null by 1.4 seconds (taking 82% of the previous time).
Update for move_iter -> into_iter rename
Add a plain-text version of the XML grammar