Changed default bindings from F7/F8 to F3/F4.

Changed default bindings from F7/F8 to F3/F4.
Changed default binding of C-x e to kmacro-end-or-call-macro.
(kmacro-call-repeat-key, kmacro-call-repeat-with-arg): New custom
variables.
(kmacro-get-prefix-arg): New function.
(kmacro-repeat-on-last-key): Renamed from kmacro-repeat-loop and improved.
Callers changed.
(kmacro-call-macro): Repeat macro by repeating last key or
key defined in kmacro-call-repeat-key.  New third arg non-nil
means to end current macro.
(kmacro-end-or-call-macro): Call kmacro-call-macro appropriately
to get repeat last key functionality.
(kmacro-start-macro-or-insert-counter): Improve doc string.