Rename modules attribute to module_files for clarity

It's a list of files that have modules, not actually the modules.
Increase the size param when testing release files

To avoid the confusion of why the 11th file isn't being returned.
Reverse got/expected args in release attributes test
Test expected modules in a release
Fix bug in log message about number of files

Previously it always logged zero and the variable that wasn't zero was never used.
Test that we index modules that start with a BOM
Comment on how we change MM's $PKG_REGEXP
Tidy :-P
Allow a BOM to precede the package declaration

There may be a way to use the file's encoding and not have to do it this way
but currently we're reading the file in binary mode and I don't want to toy
with changing that at the moment.  This should fix a few dists in the meantime.

Fixes #227.
Fixes cpan-api/metacpan-web#956.