Parses URLs and implements query escaping.
URL parser and builder, transplanted from net/url in Golang.
Most of the APIs are the same as net/url in Golang, you can check out those usages in url package - net/url - Go packages.
But there is a difference in Values.
In net/url, you can use func (Values) Get to get the first value associated with the given key,
but in this urls tool, because I implemented Values by extending HashMap, I decide not to override the get() method,
so you can use the get() method to visit values associated with the given key just like the syntax v["given_key"] in Golang.
Accordingly, I added a value() method to allow you to get the first value in Values so you can use the value() method to do the same thing as the function func (Values) Get in Golang.
Also, there's a difference in URL.
In net/url, you can use func (*URL) String to get the valid URL string, but in this urls tool, I decide to override the toString() method to do the same thing.
So, the toString() method will not describe the URL object itself.