rename #given? and #given to #has? and #direct

Mothership should not expose 'given' as the terminology here, as that term
specifically refers to the raw input strings from the user. These two
methods deal both with these 'given' values and resolved input values (via
Inputs#[], or by having one passed via #invoke).

This also frees up #given as a simple attr_reader, alongside #inputs.
bump to 0.5.0