Rename class to be more logical given practical usage

--HG--
rename : ValueUtils/HashFuncFactory.cs => ValueUtils/HashFuncFor.cs
Test skeleton
Reduce line lengths again
Rename class to something hopefully more logical.

Also provide type-inference friendly wrapper.

--HG--
rename : ValueUtils/HashFuncFor.cs => ValueUtils/FieldwiseHasher.cs
Fix syntax error
Implement a few basic sanity tests of the FieldwiseHash

--HG--
rename : ValueUtilsTest/HashFuncForTest.cs => ValueUtilsTest/FieldwiseHasherTest.cs
xUnit.net tests must be public to be runnable
minor:whitespacing
Add notes for why this struct was constructed as is
Add more tests; implement Tuple tests