Load "cl" package without "eval-when-compile" (Closes: #27)

The problem is basically that e.g. `every` is just an alias for `cl-every` and these aliases seems to be no longer known when using `eval-when-compile`. So there are two possible solutions:

1. Require **cl** without using `eval-when-compile` (this pull request)
2. Refactoring the whole package to use the proper function names e.g.
  * `every` → `cl-every`
  * `position` → `cl-position`
  * […]

Since a lot of other package already requiring **cl** in this way, it seems to be legit.