Add unittest

Add unittest

[   17s] + ./rgb
[   17s]
[   17s] running 20 tests
[   17s] test alt::gray ... ok
[   17s] test bytes ... ok
[   17s] test internal::convert::converts ... ok
[   17s] test internal::convert::array::convert_array ... ok
[   17s] test internal::convert::tuple::converts ... ok
[   17s] test internal::ops::test::sum ... ok
[   17s] test internal::ops::test::test_add ... ok
[   17s] test internal::ops::test::test_add_assign ... ok
[   17s] test internal::ops::test::test_mult ... ok
[   17s] test internal::ops::test::test_mult_assign ... ok
[   17s] test internal::ops::test::test_sub ... ok
[   17s] test internal::ops::test::test_sub_assign ... ok
[   17s] test internal::rgb::rgb_test::sanity_check ... ok
[   17s] test internal::rgb::rgb_test::test_fmt ... ok
[   17s] test internal::rgba::bgra_test ... ok
[   17s] test internal::rgba::rgba_test ... ok
[   17s] test into ... ok
[   17s] test rgb_works ... ok
[   17s] test rgba_works ... ok
[   17s] test sub_floats ... ok
[   17s]
[   17s] test result: ok. 20 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.03s