man: Makefile produce mdwn for ikiwiki

Signed-off-by: Jean Privat <jean@pryen.org>
man: add .gitignore

Signed-off-by: Jean Privat <jean@pryen.org>
man: update nitg because of #873

Signed-off-by: Jean Privat <jean@pryen.org>
man: rewrite the documentation of the other tools

Signed-off-by: Jean Privat <jean@pryen.org>