support running without config
add support for dmenu and improve support for last

cons can now select item to perform action on via dmenu. For example,
"cons -", "cons - new", and "cons keep -".

cons now handles last in a way that works with more actions. For
example, "cons last", "cons keep last", and "cons rm last".

files tags are no longer remembered in files such as LAST_FILE and
LIST_CACHE. This should fix bugs when you edit tags manually by renaming
files.

Tabs were removed from output because they don't look good in dmenu. The
justification might come back in the future as spaces done with format.
increment version to 0.3.0