Add wd-values command

[nichtich]

As suggested in #6 (comment) a command similar to wd-claims to only get statement values.

[maxlath]

couldn't that simply be an other option on wd-claims?

$ wd claims Q2112 P625 --format values
52.016666666667 8.5166666666667
$ wd claims Q2112 P625 --format degrees
52°01'0.00" 8°31'0.00"

[nichtich]

In fact. We can still create an alias later.