Removed paredit keybindings from custom.el.

They were conflicting with Org-mode-- unacceptable!
Bind smartparens with sp-use-smartparens-bindings.

The function sp-use-smartparens-bindings sets up the key bindings to
smartparens functions to the same values as seen in the examples on
https://github.com/Fuco1/smartparens/wiki/Working-with-expressions, but
does not interfere with Org Mode (like the paredit bindings).