Create a Term from arbitrary Read and Write pair

[argv-minus-one]

Currently, a Term can only be created from stdin and either stdout or stderr. This covers the most common case, but is rather inflexible.

The issue I'm running into is that I can't mock user interaction with my program (which uses dialoguer) in a test case, because there's no way to create a Term that's connected to mock I/O streams.

Another possible use case is interacting with a user through a socket. For instance, a Rust program might contain an embedded SSH server and interact with users that way.

Please consider allowing the creation of Terms connected to arbitrary Read and Write implementations, or at least arbitrary file descriptors/handles.

[mitsuhiko]

I would accept a patch for this.

[stuhood]

Related: I'd like to be able to open for an arbitrary RawFd... Term currently implements AsRawFd, so perhaps the relevant bounds here would be Write + AsRawFd?

I can take a swing at the patch if so.

[pksunkara]

Go ahead.

[stuhood]

Thank you. Will try to start this next week (unless someone beats me to it!)

[stuhood]

Have started.

[stuhood]

Hey folks! Would appreciate review on #93 when you get a chance.