added acos, tan and asin builtins
added acos, tan and asin builtins

tias/libminizinc,jjdekker/libminizinc,jjdekker/libminizinc,nathanielbaxter/libminizinc,nathanielbaxter/libminizinc,nathanielbaxter/libminizinc,nathanielbaxter/libminizinc,jjdekker/libminizinc,tias/libminizinc,jjdekker/libminizinc