Vendor dependencies

Let's see how I like this workflow.

vendor/crossterm/src/error.rs

@@ -0,0 +1,8 @@
+//! Module containing error handling logic.
+
+use std::io;
+
+/// The `crossterm` result type.
+pub type Result<T> = std::result::Result<T, ErrorKind>;
+
+pub type ErrorKind = io::Error;