Cleaned up codebase and changed "from" keyword argument.

I fixed some various errors with the codebase such as typos, missing imports, and unused variables.

I also proposed a fix for using from as a keyword argument since from is a reserved keyword.
See this code to reproduce bug:

    from datetime import datetime
    from calendar import timegm
    from pingdomlib.pingdom import Pingdom

    username = "username"
    password = "password"
    api_key = "api_key"

    pingdom = Pingdom(username, password, api_key)
    checks = pingdom.getChecks()

    # 'from' is a reserved keyword and will not work as a keyword argument
    outages = checks[0].outages(
        # Should have a syntax error on the line below.
        from=timegm(datetime.utcnow().utctimetuple()) - 86400,
        to=timegm(datetime.utcnow().utctimetuple())
    )

By using `from_` instead of `from` we can get around the syntax error caused by using `from` as a keyword argument.