Use better arguments for API calls.

- Update the readme with argument usage.
Handle additional arguments for List API call.

- Add ability to handle offset and count for List API call.
- Update readme with additional arguments usage.
Make readme section of using the Client more readable.
Add command to get Steps from last 14 days.

- Refactor parts of the client class.
- Add ability to get the last 14 days worth of steps and output as JSON.
- Update readme with new command.
Handle start and end date parameters with list API call.

- Add arguments to take the startDate and endDate optionally.
- Add logic to not use count and offset if startDate and endDate are used.
- Update readme to explain the usage of startDate/endDate and explain special notes about the API.