trurl: add --trim

[bagder]

--trim can remove (parts of) components. Starting out with query support for removing specific "tuples".

Man page and README updates. Added test cases.

Fixes #50

[ijoseph]

This is so powerful! We can now do something like:

    trimmed=$(trurl "$url" --trim query='utm_*')
    trimmed=$(trurl "$trimmed" --trim query='fbclid*')
    trimmed=$(trurl "$trimmed" --trim query='notif*')
    trimmed=$(trurl "$trimmed" --trim query='ref*') 

It's a bit whack-a-mole, but like with AdBlock, ad campaign tracker prefixes could be crowdsourced. Love it.

[bagder]

You can also do any amount of --trim actions on the same command line.