Fix #3
distribution functions do not need to follow <-
cdf function keywords don't need to follow a <-
Revert "Fix #3"

This reverts commit 8fef2dbb028127223b6b69e509fbc53f7647a188.
Fix #3 (for real)

- fix stan-regexp-opt to add grouping parentheses
- also adjusted cdf and distribution functions so they don't need to
  follow <-
Merge pull request #4 from stan-dev/fix-issue-3

Fixes #3