Basic support for manpages in multiple languages

Basic support for manpages in multiple languages

The patch changes the path where the manual pages are compiled, resulting in
a tree structure that follows the man-db convention: the man pages of each
language are stored in a subdirectory of the main man path. For example, the
input file "$AWESOME_SRC/manpages/awesome.1.fr.txt" would be compiled as
"$BUILD_DIR/manpages/fr/man1/awesome.1". The installation step just copies
the resulting directory (in the example, "$BUILD_DIR/manpages/") into the
global man path of the system, excluding the temporary files.

The input .txt files for the translations are not added directly to
AWE_MAN_FILES: instead, the new variable AWE_MAN_LANGS stores the language
names and their input file names are generated automatically. The main
reason of this modification is that it was more convenient for my testing
purposes: this behaviour can be changed back with minor modifications to the
code. This patch is supposed to be a first draft, after all, and it is far
from being perfect, but I hope it is of help.

Signed-off-by: Diego Moreda <diego.plan9@gmail.com>
Signed-off-by: Julien Danjou <julien@danjou.info>