Reuse BaseBenchmarks infrastructure

[ViralBShah]

Its important to reuse as much of BaseBenchmarks and JuliaCI infrastructure as possible, and perhaps even merge this in there, if we get a good body of large user codes in here.

@jrevels I may need your help to structure this right from the beginning.

[jrevels]

It should probably wait a week or two while I finish developing/testing the new approach to solving our variance problems. Until I can confirm the viability of the results, it makes sense to hold off on proliferating the infrastructure to external packages. (cc @KristofferC, since you've already written some benchmarks with BenchmarkTrackers.jl).

Is the idea for IndexingBenchmarks.jl to incorporate benchmarks just from Base, or from external packages as well? If the former, these examples should eventually end up in BaseBenchmarks.jl, otherwise I can open up a PR here at a later date to apply the benchmarking framework to IndexingBenchmarks.jl.

[ViralBShah]

The intent is to collect as many user codes I can lay my hands on for the purpose of indexing benchmarks.