GitLab

With verbose flag:
* remove EnableStdin() flags on all StringArg,

* remove all unneeded parsing code for StringArg, and print an
* informative message if `ipfs` begins reading from a CharDevice,

* remove broken go tests for EnableStdin cli parsing, and add some
* trivial test cases for reading FileArg from stdin,

* add a panic to prevent EnableStdin from being set on
* StringArg in the future.

Resolves: #2877, #2870
License: MIT
Signed-off-by: Thomas Gardner <tmg@fastmail.com>