Add some more float builtins (ln, log2, exp, pow)
Add some more float builtins (ln, log2, exp, pow)

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