* add sample multipart withBodyContent

* add extension methods for stringcontent and file (via path)

* redown netstandard 2.0 + add from stream

* AddFile bytes, change to reuse stream instead async + dispose

* CL + readme + cleanup

* bump version

* add simple http client doc

* optional mimeType + auto resolve from fileName

* update typedoc + remove mimeType from test

* update todo