Add Sum256 and Sum224 no-allocation functions

[teknico]

The New and Sum methods, part of the Hash stdlib interface, allocate memory on the heap. The stdlib sha256 package uses a different method, Sum256, that does not allocate memory.

This change adds two functions, Sum256 and Sum224, and optimizes the code so that calling them does not allocate any memory on the heap. The standard New+Write+Sum API allocations are also reduced:

$ go test -benchmem -bench .
goos: linux
goarch: amd64
pkg: github.com/teknico/blake256
Benchmark1K-8          300000   3821 ns/op  267.99 MB/s  144 B/op  1 allocs/op
Benchmark8K-8           50000  28272 ns/op  289.75 MB/s  144 B/op  1 allocs/op
Benchmark64-8         3000000    550 ns/op  116.30 MB/s  144 B/op  1 allocs/op
Benchmark1KNoAlloc-8   300000   3737 ns/op  273.98 MB/s    0 B/op  0 allocs/op
Benchmark8KNoAlloc-8    50000  28334 ns/op  289.11 MB/s    0 B/op  0 allocs/op
Benchmark64NoAlloc-8  3000000    506 ns/op  126.40 MB/s    0 B/op  0 allocs/op

New tests and benchmarks are also added, and the tests package is made different from the code one. The tests do not need access to code internals anyway.

[dchest]

Thanks! This looks good apart from test (see comments)

[dchest]

Hmm...

[teknico]

Ouch, sorry, will fix it.

[dchest]

Don't rename please.

[teknico]

Will revert if you want me to. Care to mention why, though?

[dchest]

I just like the simplicity of it, I guess 🤷‍♂

[teknico]

Well, this way tests cannot change code internals, which makes them more effective (blackbox vs. whitebox testing, basically). But again, happy to revert if you don't like it.

[dchest]

Sure, but it's a few letters more to type for a theoretical benefit! Reading the code is the best guarantee that it can't change internals :) Whatever, let's do a separate package test if you want.

[dchest]

Actually, then it would have hardcoded package path, so let's not do it.

[dchest]

Interestingly, the mistake with import in PR was caused by a having a separate test package, so I guess my kind of testing wins :)

[teknico]

As you wish.

[dchest]

Thanks again!

[teknico]

I just noticed I neglected to mention the two new functions in the README, sorry about that.

[dchest]

Ah, no worries. I should just like to godoc there instead of listing functions.