Auth: Rewrite mk_passwd in C (close #131).

This patch drops the mk_passwd python script from auth plugin, by adding an
equivalent C implementation.

The C implementation makes use of Monkey functions, whenever possible, so it
links with Monkey objects.

In order to make the linking possible, some minor modifications had to be made
to the configure script, monkey.c and mk_config.c source files.

Signed-off-by: Vladimir Cernov <gg.kaspersky@gmail.com>
Doc: CONTRIBUTING.md: specify number of chars per line

Signed-off-by: Eduardo Silva <edsiper@gmail.com>