removed min() function for RescalePair()

[cbelsole]

Removing the min() func from RescalePair() stops the copy operation for passing the values into min() saving on the bytes per op and marginal decreases in runtime. For fun I implemented the new implementation into a new Add() func and it looks like the effect is doubled.

goos: windows
goarch: amd64
pkg: github.com/shopspring/decimal
cpu: Intel(R) Core(TM) i5-3550 CPU @ 3.30GHz

BenchmarkRescalePairGreaterThan-4      	 3631178	       333.6 ns/op	     200 B/op	       7 allocs/op
BenchmarkRescalePairLessThan-4         	 3669758	       336.1 ns/op	     200 B/op	       7 allocs/op
BenchmarkRescalePairEqual-4            	261132116	         4.714 ns/op	       0 B/op	       0 allocs/op

BenchmarkNewRescalePairGreaterThan-4   	 3847358	       329.0 ns/op	     160 B/op	       7 allocs/op
BenchmarkNewRescalePairLessThan-4      	 3669552	       318.7 ns/op	     160 B/op	       7 allocs/op
BenchmarkNewRescalePairEqual-4         	255000668	         4.692 ns/op	       0 B/op	       0 allocs/op

BenchmarkAddGreaterThan-4              	 2455047	       428.4 ns/op	     280 B/op	       9 allocs/op
BenchmarkAddLessThan-4                 	 2711714	       430.2 ns/op	     280 B/op	       9 allocs/op
BenchmarkAddEqual-4                    	11634004	       100.4 ns/op	      80 B/op	       2 allocs/op

BenchmarkNewAddGreaterThan-4           	 2999233	       400.4 ns/op	     200 B/op	       9 allocs/op
BenchmarkNewAddLessThan-4              	 2975070	       402.1 ns/op	     200 B/op	       9 allocs/op
BenchmarkNewAddEqual-4                 	13229145	        97.82 ns/op	      80 B/op	       2 allocs/op

[mwoss]

Overall nice optimization, I have not thought about that during the implementation.
Sorry for not working CI, Travis.org is unresponsive. I tried to contact them a few times about open-source credits. Probably I would have to move to another open-source friendly CI service.

[cbelsole]

@mwoss I fixed the tests. Thanks for catching that.

As far as CI environments, for public projects CircleCI is pretty easy to setup and has a free tier.