lispy.el (lispy-to-ifs): add and bind to "xi"

* lispy.el (lispy--case->if): Improve.
  (lispy--if->case): New function.
  (lispy--ifs->cases): New function.
lispy.el (lispy-to-cond): add and bind to "xc"
lispy.el (lispy--eval): change arg name to str!

* lispy.el (lispy--eval-elisp): Update.
lispy.el (lispy--not-whitespace): remove
lispy.el (lispy-flatten): add and bind to "xf"

* lispy.el (lispy--replace): New function.
lispy.el (lispy-from-left): add
lispy.el (lispy-to-ifs): improve
lispy.el (lispy-to-cond): improve