Add solveset benchmarks

[hargup]

We should add solveset benchmarks to compare it with solve.

[moorepants]

@hargup You or your current gsoc student would be the best to suggest some good benchmarks. Feel free to add one or point us to some code for a good test.

[moorepants]

BTW, are you all planning to have solve call solveset eventually? If so, once that change is made, you will simply have to look at solve's bechmarks to see whether you sped up or slowed things down.