Crew specifications

Used f.i. in Experiments (used in crew_operate, crew_reset or crew_prepare as well as in some other Kerbalism modules) have to be given according to true|trait|[trait]@level

Examples:

• "true": any kerbal will do.
• "Scientist": you need a Scientist, doesn't matter how experienced. Other traits are "Pilot" and "Engineer". We're not assuming that you'll want to use "Tourist"...
• If the value is "@3" any Kerbal with 3 or more stars will do
• If the value is "Scientist@2" you need a Scientist with 2 or more stars.
• Empty values usually turn the feature off.