More feature-complete `pros::io` module.

[tropicaaal]

What's the motivation for this feature?

Currently pros::io exists to do the following things:

• Provide macros for printing data to the serial terminal.
• Re-export stuff that should be in core from no_std_io.

There are several things, especially concerning terminal interactions that could be added.

• Reimplementing io::stdin/io::stdout/io::stderr locks from std for safe raw access to the I/O writers.
• Support for stdin in general.

Describe the solution you'd like

Implement Stdin, Stdout, Stderr structs similarly to what's provided by std::io.

Describe the drawbacks, if any

N/A

Describe the alternative solutions, if any

N/A

Additional context

https://doc.rust-lang.org/stable/std/io/index.html

[tropicaaal]

Another thing we should look at is how this plays into serctl and the serial driver, which is technically part of the kernel's VFS. This would need to be thought out along with #103.