tests/Benchmark: Foarmatting and descriptiveness

* Add program/file description
* Useful error on invalid number of arguments
* Code formatting
* Make varnames descriptive
tests-files: Add description to file

* Add descriptions to files in src/tests
* Minor formatting in OverlayTest.cpp
OverlayTest.pro: Add includepaths for celt and speex

* Paths were missing from the include-path. With the celt and speex includepaths added it compiles now.