Fix some warnings and a test


  * fix `warning: implicit conversion loses integer precision: 'long' to 'int'`
  * extconf already sets `-Wextra`, no need for `-Wall`. Also add `-Wno-comment`. There will be wildcard refs or filepaths in the docs. The warning is just noise. 
  * on my machine:
```ruby
 "A\314\212ngstro\314\210m" == "Ångström" #=> false
```