Adds support to API token

[ingmferrer]

In the recent library rework, I dropped the manual integration (API Token) because I confused it with API Keys which is now deprecated by Pipedrive.

The deprecation warning says:

Warning!
As of December 2, 2019, we will be removing the Authorizations endpoint:

POST /authorizations
We deprecated this endpoint on February 28, 2019, and we strongly advise you to avoid the use of this endpoint. The /authorizations endpoint is a legacy way of authorization using generic API keys. Such an approach does not provide transparency into which applications have access to data nor the opportunity to control the permissions these integrations have. Therefore we suggest using OAuth Authorization.

In case you are using the /authorizations API endpoint in your code or 3rd party app/integration, please remove any dependency on this endpoint as soon as possible.

So this update adds the manual integration support and fix #11

Also, I've updated pypi package with this release pipedrive-python-lib==1.1.0 and updated the README. Refer to Using this library with API Token for more information.

Thanks.