Add ability to filter by attribute

[sawilde]

An attribute filter will allow code (classes/methods) to be filtered (usually to exclude) by a known attribute.

This has been a common requested feature but I am wary that code excluded by this method then gets ignored to the detriment to the code base.

I propose extending the current filters from [] => <>[]* where the <> is optional and <*> is implied if not supplied

Should consider a marker in the report file to say why it is missing perhaps.

[sawilde]

Okay, after two reverted attempts I have decided that 'fixing' the filter up front was a bad idea - I have now decided to have just a simple excludebyattribute option that will match with wildcards and handle many exclusions using a ; delimiter.