Fix beg of buffer/mark

You shouldn't use commands that set the mark to move around the buffer. I've replaced `(beginning-of-buffer)` with `(goto-char (point-min))` and removed the `push-mark` commands.

Also the `skeleton-easy-regexp-display-abbrev` function was needlessly complicated, so I've cleaned that up a bit too.

PS: this patch depends on the whitespace-fix, so merge that first.

PSS: did you consider using IDO instead of your own completition. It feels a bit slow (and also sets the mark somewhere, but I wasn't able to find where)