configure: add quiet build output
configure: add quiet build output

The benefit here is that once a tag has been used in several posts the
build output just spams the terminal and actually you don't get any
useful output, ie. you don't see the number of regenerated static pages
at all, as part of the last cmdline already fills the whole screen. Add
a silent output mode to solve this problem, which can be disabled by
'make V=1' for debugging purposes.

artagnon/rejourn