Some changes.
Deprecate init function.

1. deprecate init function in dogo.proc.
2. add a test folder/package for test work.
Add utils, custom not found handler and sth. else.

1. add utils package for some useful functions and structs.
2. make router firstly match static file server.
3. add a default not found handler and a function for easily specifying a
custom handler.
4. fix a bug: send json multiple headers write.
5. add some methods to Proc, Request and Response.
Merge pull request #3 from ggicci/dev

Fixed some bugs and did a lot of changes on code structure.