to avoid Monomorphism bloating.

Fixes Issue #62

Use Predicate file path to compare strings in path

Eq Predicate ensures equality in string path

Change eq_file function to use Predicate directly
Change tests to verify that function works

Change read_file to use AsRef<Path>
Correct fs::read to be compatible with compiler

Change to read_file so not using fs::read

remove .into()

replace path:path with path

Minimalize monomorphization bloat by using changed data type in one function
Replace concrete types for consistency with rest of code base

Does not require AsRef<Path> except in top-level function.
This is for consistency with the rest of the codebase and
minimalism of monomorphism bloat

Add AsRef<Path> to eq_file

Fixes #66

docs: Help user find predicate