Improve test execution and documentation generation

[Benjamin-Loison]

Concerning motoko: motoko/README.adoc#testing

Concerning rust:

Internet-Computer-Bitcoin-Library/rust/src/lib.rs

Lines 449 to 455 in 507c8dc

	/*
	To run documentation tests:
	1. uncomment the `use` line below.
	2. comment `#[cfg(test)]` above, above the second `use` of agent.rs, in agent.rs above `impl BitcoinAgent<ManagementCanisterMock>`, in agent.rs above `pub mod tests` and in address_management.rs above `pub mod tests`.
	3. remove the four `ignore` documentation test attribute above.
	4. add `hex = "0.4.3"` to Cargo.toml `[dependencies]`
	*/

Note that list is maybe not exhaustive.