Moved 11 functions from sequencetools to mathtools

OLD:

    sequencetools.is_fraction_equivalent_pair
    sequencetools.is_integer_equivalent_n_tuple
    sequencetools.is_integer_equivalent_pair
    sequencetools.is_integer_equivalent_singleton
    sequencetools.is_integer_n_tuple
    sequencetools.is_integer_pair
    sequencetools.is_integer_singleton
    sequencetools.is_n_tuple
    sequencetools.is_null_tuple
    sequencetools.is_pair
    sequencetools.is_singleton

NEW:

    mathtools.is_fraction_equivalent_pair
    mathtools.is_integer_equivalent_n_tuple
    mathtools.is_integer_equivalent_pair
    mathtools.is_integer_equivalent_singleton
    mathtools.is_integer_n_tuple
    mathtools.is_integer_pair
    mathtools.is_integer_singleton
    mathtools.is_n_tuple
    mathtools.is_null_tuple
    mathtools.is_pair
    mathtools.is_singleton

CHANGE: should be noted in the 2.15 change log.