Refactor message printing

Feed all those little progress and status messages through a central
place where such things as newlines, indentation, and suppressing
output when not on a TTY can be taken care of once and for all.

This patch takes care of almost, but not quite, all output. The most
notable leftover is the printing of help messages.

Signed-off-by: Karl Hasselström <kha@treskal.com>