Allow multiple input files for the CLI

[pheyvaer]

The different files are appended, so it's up to the user to make sure that no duplicate keys are used for rules and prefixes. @bjdmeest What do you think?

[bjdmeest]

Shouldn't we then add warnings that duplicate keys for rules and prefixes are found? Just for our own ease of debugging sake ;) Otherwise, sounds more than good to me!

[pheyvaer]

Yes good idea!

[vemonet]

Would it be possible to support wildcards when providing the files to process?

To run the yarrrml-parser on all .yarrr.yml files in a folder:

yarrrml-parser -i *.yarrr.yml -o .

The output files could be in the folder provided by -o with the extension being changed from .yarrr.yml to .rml.ttl

Not sure about how the output filenames, maybe introducing a different arg for a template output filename for maximum flexibility