Support for v8 API

I've updated the code to support the toggl v8 API. I've like the simplicity that your code gave to the core functions and I'm trying to stick with that. I'm actually pretty new to python, so I'm relying heavily on what you wrote before.

Big changes
* v8 API needs a project id when starting a time entry with a project, so I need to lookup project ids with project names
* the new API still requires ISO8601 formatted dates, but they can be in any time zone, so I had to manipulate the date limits when listing recent time entries. I rely upon the timezone from .togglrc
* Moved the readme to markdown and modified it some

I'll probably add displaying the client and maybe support for tags (I like the concept, but don't use them very often).