Change C-c SPC to C-c j to avoid a conflict in org-mode

In org-mode C-c SPC is bound to `org-table-blank-field`
Bind ace-jump-mode to s-. as well
Mention guru-warn-only
Merge remote-tracking branch 'origin/master' into prelude

* origin/master:
  Mention guru-warn-only
  Bind ace-jump-mode to s-. as well
  Change C-c SPC to C-c j to avoid a conflict in org-mode