Make evil-space-setup accept symbols and forms

[hlissner]

• KEY, NEXT and PREV can now be function symbols or forms that evaluate to a function (as well as a string).
• Now prints error messages if a key can't be found or is invalid.
• Remove fboundp checks so later mappings can override earlier ones.
• Delegates are now named evil-space--<function name> instead of evil-space-<letter>, e.g. evil-space--evil-snipe-f. This removes the possibility of collisions.

For example, these will do the same thing and both will work:

(evil-space-setup "f" ";" ",")
(evil-space-setup evil-find-char evil-repeat-find-char evil-repeat-find-char-reverse)

(This change was for cases where KEY, NEXT and PREV are in different keymaps)

[linktohack]

Thanks @hlissner for implementing this :+1:

[hlissner]

And done!

[linktohack]

Great! Thanks so much for this feature, @hlissner!