Fix inconsistencies in javadocs.

These changes were made with consistency in mind, in relation to the rest of the project:
 - Change self-closing <p/> tags to regular <p> tags.
 - Add missing <p> tags.
Merge pull request #160 from dlam/master

Fix inconsistencies in javadocs.
Remove usage of HTTP constants class from Apache dependency.
Relax enforcement of UTF-8 and use the body charset for decoding.

Consumers wanting well-behaved endponts should override or add to their `toBody` charset enforcement:

```java
String charset = Utils.parseCharset(body.mimeType());
if (!"UTF-8".equalsIgnoreCase(charset)) {
  throw new ConversionException("Invalid charset " + charset + ". Must be UTF-8");
}
```

Closes #163.
Merge pull request #164 from square/jw/charset

Relax enforcement of UTF-8 and use the body charset for decoding.
Make Utils constructor private.
Add response object to callback success.

Gives access to response headers while still converting response within retrofit.
Fix wrapper scope and callback param ordering.
Make response wrapper members final.
Merge pull request #165 from jjNford/master

Always return response object on success callbacks.
Merge branch 'master' of git://github.com/square/retrofit