main, parts: Allow kwargs for holster() and bare_holster().
parts: If returned a callable, open the escape hatch.
Update changelog.
setup: 0.2.3.
views: Patch up HTML template.

If the mapping/sequence's keys don't have values, then don't attempt the
recursion.

This removes superfluous colons after list items. It also removes a lot of
extraneous runtime checks for recursion onto undefined names, which are
harmless but chew up cycles.
readme, setup: Make a cut. 0.2.4.