Minor fixes and Windows improvements

• If you used a non-integer string as an array index when doing a lookup with
  MMDB_get_value, MMDB_vget_value, or MMDB_aget_value, the first element
  of the array would be returned rather than an error. A
  MMDB_LOOKUP_PATH_DOES_NOT_MATCH_DATA_ERROR error will now be returned.
  GitHub #61.
• If a number larger than LONG_MAX was used in the same functions,
  LONG_MAX would have been used in the lookup. Now a
  MMDB_INVALID_LOOKUP_PATH_ERROR error will be returned.
• Visual Studio build files were added for unit tests and some compatibility
  issues with the tests were fixed.
• Visual Studio project was updated to use property pages. Patch by Andre.
  GitHub #69.
• A test failure in t/compile_c++_t.pl on new installs was fixed.