bench hit ratio updates

[karlmcguire]

• ARC and LIRS trace file parsing
• cache configs matching @dgryski's cachetest, hit ratios matching as well
• move hit ratio tests to single thread/goroutine
• decoupled Policy stats collection from ristretto package (fixing bench fails to build #34)
• improved Clairvoyant/Optimal Policy because we're running massive ARC traces and it needs to be fast (it should be O(n lg n))
• documentation of sim package, a start to comprehensive documentation

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This change is 

[manishrjain]

Remember to add a README about how to use these benchmarks.

Reviewed 13 of 13 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @karlmcguire)

[karlmcguire]

Reviewable status: 10 of 14 files reviewed, 1 unresolved discussion (waiting on @golangcibot and @manishrjain)

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bench/cache.go, line 49 at r1 (raw file):

Previously, golangcibot (Bot from GolangCI) wrote…

S1019: should use make(map[string]uint64) instead (from gosimple)

Done.

[karlmcguire]

Dismissed @golangcibot from a discussion.
Reviewable status: 10 of 14 files reviewed, all discussions resolved (waiting on @manishrjain)

[karlmcguire]

Reviewed 10 of 13 files at r1, 4 of 4 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved