Document standard library
Document standard library

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