Added multipart param, to be used in post request (harmless otherwise)

basic usage:
r = requests.post(url, data=data, multipart=True)

it will behave same as
r = requests.post(url, data=data, files={'filename':data})
whithout having  ----> ; filename="filename" <----- in the Content-Disposition's multipart body

this somethimes will not be accepted:
Content-Disposition: form-data; name="data"; filename="filename"

this it should:
Content-Disposition: form-data; name="data"