Changes :
- Feature : Polymorphism, transform a Header object to its corresponding subclass. #26
- Feature : Implement pop() and popitem() methods in Headers.
- Bugfix : Discard multiple entries detection if the header is 'Subject'.
- Bugfix : Acknowledge the folding LF + 1 space technique to unfold.
- Add : Cookie custom header class in builder.py.
- Bugfix : Fix how WwwAuthenticate custom header is built.
- Feature: Add unfolded_content property to Header class.
- Other : Provide scripts for developers. #24