Validate API examples. Rename files

If you define a rule for a file which doesn't exist the test won't fail. If you don't add a rule for a file which exists in one of the rootDirs then it will fail.
Comparing length doesn't do much, because they can have the same length but the elements may be different.

To solve the first problem I check if all file names from `expected` are in `files`. So, I iterate over  the `expected` maps keys, and then I  search for each key/expectedFileName in `files`.