Merge branch 'release/3.2.0'

update CHANGELOG

increase version

update init

update README

add api key usage at README

update README format

add new methods/endpoints to README

update ndfts tickers function name

support demo_api_key in requests

add key endpoint/method

update new endpoints/methods

Merge remote-tracking branch 'origin/master' into develop

Merge pull request #80 from jakoooob/patch-1

Merge pull request #87 from arielen/master