Need setting for Meta modifier

There is currently no setting to specify the Meta modifier. One might expect to be able to configure such a setting in sakura.conf.

It's possible to specify the Meta modifier in URxvt via its command line arguments. From urxvt(1):

    -mod modifier

    Override detection of Meta modifier with specified key: alt, meta, hyper, super, mod1, mod2, mod3, mod4, mod5; resource modifier.

One could, for example, set Super as the Meta modifier by adding the following line to ~/.Xresources:

    URxvt.modifier: super

For additional detail, see this discussion: https://answers.launchpad.net/sakura/+question/679521.