Add a fromObject method to FormUrlEncodedRequest

[KPull]

Similar to #21, we need to add a fromObject() method to the FormUrlEncodedRequest class. This will serialize the given object into a URL encoded string to be sent with the request.

[FrelliBB]

How do you propose we do this if given anything that contains some form of nested objects? Should we just take the root object fields and serialize their values with #toString?

[KPull]

Nested field properties will have their names separated with a dot. So:

class Name {
    public String first;
    public String last;
}

class Person {
    public Name name;
    public int age;
}

Person would serialize:

name.first=john&name.last=doe&age=27