Add additional BLS benchmarks

[StephenButtolph]

Why this should be merged

1. Clarifies a couple confusing comments.
2. Adds additional benchmarks.

How this works

^

How this was tested

BenchmarkPublicKeyToCompressedBytes-12             	 8733057	       136.5 ns/op	      48 B/op	       1 allocs/op
BenchmarkPublicKeyFromCompressedBytes-12           	   23743	     50507 ns/op	      96 B/op	       1 allocs/op
BenchmarkPublicKeyToUncompressedBytes-12           	 6946160	       174.2 ns/op	      96 B/op	       1 allocs/op
BenchmarkPublicKeyFromValidUncompressedBytes-12    	 3998372	       297.9 ns/op	      96 B/op	       1 allocs/op

Need to be documented in RELEASES.md?

No.