Support Chardet version 4

[dwt]

It was released yesterday: https://github.com/chardet/chardet/releases and I would like to use it together with requests.

[bignose-debian]

Someone will need to investigate how to test compatibility of Requests with the new chardet version.

[mishankov]

PR for this is already in progress
#5688

[nateprewitt]

#5688 is merged. It should be available in the next release.