simpler
Merge pull request #781 from joaojeronimo/master

simpler isReadStream function
Provide ability to override content-type when `json` option used

Fixes #784
Merge pull request #785 from vvo/784-fix-json-content-type-override

Provide ability to override content-type when `json` option used
Adds content-length calculation when submitting forms using form-data library. This is related to issue 345.
Merge pull request #793 from Juul/master

Adds content-length calculation when submitting forms using form-data li...