Libddog

- Made a small redesign of `ddog dash list-live`. Issue 52.
- The `AUTHOR` column has been renamed to `USER` and now shows either the user
who created the dashboard marked with `[c]`, or the user who last modified
the dashboard marked with `[m]`. The modifying user is preferred and is
detected using the dashboard description. Failing that, the creating user is
shown.
- The `CREATED` column showing the creation timestamp has been removed since
the age of the dashboard is not really that relevant and does not tell us
whether it's still used or not.
- The `MODIFIED` column has been renamed to `TIME` and has been abbreviated to
use less horizontal space.
- A `LIBDDOG` column has been added, showing the version of libddog that was
used in the last modification of the dashboard. This is detected using the
dashboard description.

- The dashboard description footer now also includes the userid of the user
whose credentials were used in the update. Issue 38.

- Swap out datadog client library. This removes the dependency on the `datadog`
package, which is now considered legacy by Datadog. The new client is a thin
http client using `requests` directly. Issue 40.

- Deprecated the `title` parameter to `Request` as a way to set a label for a
query. From now on the `title` parameter can still be set, but is a noop. It
will eventually be removed. Passing `title` also raises a `DeprecationWarning`
which is printed to stderr. Issue 50.
- Added a cookbook with an entry that explains how to set the label for a query
using a `Formula`.

- Added validation to make sure that all query names in a `Request` are unique.
The validation runs when the `Request` is constructed. Formula validation now
also runs at `Request` construction time, to avoid a latent error. Issue 45.

- Added an upgrade-check in the cli. When using the cli it checks the installed
version against the latest version in PyPI and gives instructions on how to
upgrade. The check is not repeated for the next 24h. The flag
`--no-upgrade-check` tells the cli to skip the check.