Teams API: support description & privacy fields

[mgorny]

Per https://developer.github.com/v3/orgs/teams add support for the description & privacy properties of teams. The former is quite useful, and the latter is pretty much required these days since teams are secret by default.

I'm sorry but I can't figure out how to add tests properly.

[sfdye]

@mgorny LGTM, would you mind just adding some unit tests and I will merge!

[mgorny]

I'm sorry but it's been 1.5yr and I don't have time anymore to figure out how to properly record stuff for tests to work just to add two missing properties to package I use once a month, with my local patch, for 1.5yr already. I've tried to follow the instructions, I've got the following exception and I see no purpose in trying further.

======================================================================
ERROR: testAttributes (github.tests.Team.Team)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "github/tests/Team.py", line 40, in setUp
    self.org = self.g.get_organization("BeaverSoftware")
  File "github/MainClass.py", line 214, in get_organization
    "/orgs/" + login
  File "github/Requester.py", line 185, in requestJsonAndCheck
    return self.__check(*self.requestJson(verb, url, parameters, headers, input, cnx))
  File "github/Requester.py", line 231, in requestJson
    return self.__requestEncode(cnx, verb, url, parameters, headers, input, encode)
  File "github/Requester.py", line 284, in __requestEncode
    status, responseHeaders, output = self.__requestRaw(cnx, verb, url, requestHeaders, encoded_input)
  File "github/Requester.py", line 309, in __requestRaw
    requestHeaders
  File "github/tests/Framework.py", line 100, in request
    self.__writeLine(input.replace('\n', '').replace('\r', ''))
AttributeError: 'NoneType' object has no attribute 'replace'

[sfdye]

@mgorny Sorry for the delay. Good news this issue has been fixed in the master, so it should be okay to record test data. But I totally understand if you don't to continue anymore, in which case feel free to close this PR.