Suggest adding no_main for error[E0601]

[ascjones]

Since #1076, no_main is now required. This PR adds a suggestion in case of the error error[E0601]: main` function not found in crate...

This is the result:

Note that the suggestion must appear before the compiler error because we can't know for sure how many lines the error message will encompass, so we just print it first.

Introduces duct which allows for easily building command expressions and working with capturing the stdout and stderr.

Maintaing the progress bar

An earlier iteration was using BufReader::lines to read the captured stderr and check for the error code for the missing main function. However this came with the downside of the familiar progress bar (see below) not being displayed.

I have been able to get that to work again with some hacking. The result involves reading the reader one byte at a time and redirecting that straight to stderr, while maintaining a small buffer to check for the known error. I am aware that this is not the most efficient way, but it was the only way to get the progress bar displaying as it does when not capturing stderr.

[cmichi]

As discussed via dm, let's omit the tail end of the error output and exit like this:

$ cargo contract build
 [1/*] Building cargo project
   Compiling flipper v4.2.0 (/private/var/folders/s5/5gcp8ck95k39z006fj059_0c0000gn/T/cargo-contract_zJEp2z)

Exited with error: [E0601]
Your contract must be annotated with the `no_main` attribute.

Examples how to do this:
  - #![cfg_attr(not(feature = "std"), no_std, no_main)]
  - #[no_main]

(with the last part in red)

[ascjones]