Implement/derive Eq+PartialEq for more types

[filips123]

This PR is very similar to #128 and can replace it, because it also implements/derives Eq+PartialEq traits for more (I think all) public types. Reasons for this are the same as in #128, but I applied them to more types.

The main types where I think that is useful (apart from Mime) are MediaType and MediaRange (to allow matching them and using them in structs that also want to implement Eq) and ParseError (to allow matching specific errors), but I hope adding Eq+PartialEq to more types won't hurt.

[bsodmike]

@kailan can you please merge this, ugh I'd hate having to fork this crate.

[kailan]

@bsodmike I'm not a maintainer unfortunately