combo: swap meaning of top/bottom meet/join

"Es ist Deutschland hier" so we use the european style interpretation of
top/bottom.
fix comment
refactor/improve gen_docu script

This mainly allows us to use external templates like the ones used for
homepage.
iropt: recognize multiplication with power-of-2 as Shl behaviour
Correct combo: 0 - x does not have the same value as x.
Remove unnecessary special case for labeled blocks from combo.

IJmp supplies its successors with reachability information.
It is not necessary to force all labeled blocks to reachable.
convopt: changing the mode of Unknown is cheap
iropt: make sure we don't miss Ors in is_Eor_Add
combo: Remove the redundant check, whether the block of the Phi is reachable from compute_Phi().

compute() does this check already before calling compute_Phi().