Improve tor_sscanf tests

Improve tor_sscanf tests

* Add many new test cases, tweak/improve existing ones, reorganize them a bit
* Switch the parameters in all test_eq calls so the expected value is the first
* Change all the "r = tor_sscanf(...);\ntest_eq(1, r)" to the more compact
  "test_eq(1, tor_sscanf(...))". It may be a tiny bit harder to find the
  tor_sscanf calls (it's the long lines anyway), but it saves a lot of lines,
  which should help readability.