Remove non-standard comma-separated query parameter parsing

[reynir]

The order of parameters, presence/absence of =, and use as a list in a single parameter (?a=1,2,3) or multiple parameters (?a=1&a=2&a=3).

There are two reasons for this:

1. The only reliable equality on URIs is per-character and so we would like access to parsed values that retain a similar equality; however, this doesn't prevent convenience functions.
2. Some query-like interfaces distinguish between simple presence of keys and keys with values. For instance, http://erratique.ch/software/cmdliner/doc/Cmdliner.Arg.html#VALopt turned into a query string interface could have this behavior.

I made a design mistake back around 1.3 or so when I introduced the "handy" comma-separated list query value form. This makes collecting duplicate values for the same key harder than it should be and is almost completely unnecessary. I did it because I wanted to avoid a string option option type somewhere. It will be removed in 2.x (which I've been meaning to get to for over a year now...). Properly doing a 2.x design, clean-up, and test will probably require a couple weeks full time. I'm open to suggestions or pull requests for a 2.x branch.

Originally posted by @dsheets in #61