An assortment of enhancements for clar2

First off, sorry to group all this in one PR. Feel free to cherry pick what you like. I've tried to group it into intelligible commits so you shouldn't have to take it all.

Really I had two goals here:

* Get the `-l` option output in sorted order
* Make the `-s` option allow test suite prefix names to be used, so I could use `libgit2_clar -sstatus::` to run all of the status tests.

I ended up also:

* writing a small test suite for clar itself so I could try out my modifications,
* cleaning up some formatting (mostly for `clar.suite` which really doesn't matter, I know, but I was reading it so I cleaned it up),
* and as I wrote the test suite, I was wondering what I should do about copyright headers, so I ended up updating that as well.

I think there are only two "controversial" items in this PR:

1. I made it so that when you use `-s` with a suite prefix match, clar will print the names of the matched test suites in the output. This is my personal preference, but I can imagine that you might prefer to keep the output simple even in this case. This change is completely isolated in a single commit, so you can drop it easily if you must.
2. The Makefile I wrote for the test suite is amateurish, but I just wanted to get something working. Feel free to write something better. I needed to get the absolute path for the fixtures; there is probably a better way than what I ended up doing.