Update tinymt32_nif_tests.erl

* Add function specs
* Add ran() type from random module
* Fix test_speed_orig_uniform_rec1/5 to call itself
  (formerly calling test_speed_orig_uniform_n_rec1/5)
  (Note "uniform_n", which is incorrect)
Update README.md

* Document the bug found by dialyzer of test_speed_orig_uniform_rec1/5
  in tinymt32_tests.erl and tinymt32_nif_tests.erl