Dynamic menus

[maxatome]

• Introduce f.label function, a left aligned unselectable menu item
• Introduce multiline strings using triple double-quoting
• Introduce f.dynmenu function and so dynamic menus

Example of use with these 3 features mixed together:

f.dynmenu """
cat <<EOF
"$(hostname)"                    f.title
"*$(date)"                       !"daemon xterm"
"Details..."                     f.dynmenu "/usr/local/bin/another_menu.sh"
"Battery level $(battery level)" f.label
"Another info $(get_info)"       f.label
"Shutdown" ("white":"red")       !"shutdown -r now"
EOF
"""