ftp/cpr: Add cpr 1.6.2

C++ Requests is a simple wrapper around libcurl inspired by the excellent Python
Requests project.

Despite its name, libcurl's easy interface is anything but, and making mistakes
misusing it is a common source of error and frustration. Using the more
expressive language facilities of C++11, this library captures the essence of
making network calls into a few concise idioms.

WWW: https://whoshuu.github.io/cpr/
WWW: https://github.com/whoshuu/cpr