Add complete Pipes.Prelude benchmarks.

Previously there were two modules for this single benchmark because I did not know that running ``` cabal bench ``` without a benchmark name will run all benchmarks and I had in mind to do an ``` all-benchmarks ``` benchmark module.

I lowered the minimum ``` Cabal  ``` version to 1.10, and that's the minimum version required for the ``` Default-Language ``` option.

I grouped ``` enumFromTo ``` and ``` each ``` but I really don't like the name I gave the group.

``` runIdentity ``` is used a lot and I really don't know if I should make a shorter synonym or not.

I left a few function from Pipes.Prelude out because I'm not sure how to benchmark them.

Please take a look when you have the time and let me know if the benchmarks are appropriate, and other stuff.