Added wc-reset to goal setting

* wc-mode.el: (wc-reset) added to wc-set-*-goal functions

Now, when a goal is set, a reset is performed on the counters for the
given buffer.

I also did a version bump for this functionality to 1.3.
Use emacs count-words function if available.

* wc-mode.el: Updated the wc-count-lines-function variable

In Emacs 24, a count-words function was supplied that is similar to the
how-many function we use here. I added a check to see if this function
is available and use it when it is bound.