Control which levels should be ouputted

[tomzx]

When calling the tool, it should be possible to specify the levels we want to display: major, minor, patch. By default, all levels would be displayed, however it would be possible for the user to say "I want only patch and minor", or "patch and major", or "major only", etc.

An interesting potential side effect could be to allow the user to sort the levels according to their own preference:

• major, minor, patch
• patch, minor, majour
• major, patch, minor
• ...