Fix partial_pathencode to properly handle asterisk `*`

[kyleboe]

Adds case and test for encoding an asterisk in the path adhering to: https://src.chromium.org/viewvc/chrome/trunk/src/url/url_canon_path.cc#l56

References

• https://github.com/edgurgel/httpoison/issues/471
• https://github.com/benoitc/hackney/issues/399
• https://github.com/benoitc/hackney/issues/277
• https://github.com/benoitc/hackney/issues/272