Separate Server and App

[CreatCodeBuild]

Some functionalities are currently in server, since I used the example curio code in h2 as a starting point.

Now I see the needs to separate these code out and put them into the app module.

server is the module which actually talks with http.
app only handles restful end point.

Users built on top of app module. They should never touch server module unless they want to implement their own app module.

[CreatCodeBuild]

The separation of code is improved. Need to remove IO functionality from EndPointHandler.

An EndPointHandler should only contains the necessary information a user need. IO should be handled by other classes or functions.

In such a way, EndPointHandler should be easier to test. Actually, if EndPointHandler doesn't do IO, it can be totally replaced by the new Stream class.

[CreatCodeBuild]

Should have separate utilities for IO. Remove EndPointHandler and replace it with Stream and separate IO functions.

[CreatCodeBuild]

Have removed endpoint module. Moved all IO to http.HTTP class.

However, the current API pass the HTTP instance to the top level user. This is a bad design. The end user should not have access to such an internal class.

A better design is to pass the end user some kind of HTTP class which only provides output utilities, aka, send methods.