Update create transaction example code

[tcharding]

Description

The transaction builder changed a while ago, looks like some of the example code did not get updated.

Update the transaction creation code to use a mutable builder.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

[afilini]

Looks like they are being ignored for some reason, can you also change them to no_run instead so that we can keep them updated going forward?

I did a quick test and there's also another test failing on line 145 which can be trivially fixed (replace None with SignOptions::default())

[tcharding]

Thanks for the review, will fix as suggested.

[tcharding]

@afilini I fixed as suggested including changing all ignores in lib.rs to no_runs (with code fixes). And, for the awesomely anal among us, I fixed the import lines to use dbk project style.

[afilini]

I think the CI is failing because the tests use the electrum stuff but they are not feature-gated. It's kinda ugly but there's a way to fix it:

bdk/src/keys/mod.rs

Lines 453 to 472 in 12641b9

	#[cfg_attr(
	feature = "keys-bip39",
	doc = r##"
	```rust
	use bdk::bitcoin::Network;
	use bdk::keys::{DerivableKey, ExtendedKey};
	use bdk::keys::bip39::{Mnemonic, Language};
	# fn main() -> Result<(), Box<dyn std::error::Error>> {
	let xkey: ExtendedKey =
	Mnemonic::from_phrase(
	"jelly crash boy whisper mouse ecology tuna soccer memory million news short",
	Language::English
	)?
	.into_extended_key()?;
	let xprv = xkey.into_xprv(Network::Bitcoin).unwrap();
	# Ok(()) }
	```
	"##
	)]

[afilini]

Since we have to do the release today and this isn't ready yet I've cherry-picked abbea4b on the release branch, so at least we will have the correct example on the published crate

[tcharding]

Wow, this opens a whole can of worms. The lib.rs inner doc comment documents behaviour from the default set of features (as one would expect) but we cannot expect folks to build with the default set of features so we do not currently build these docs. Attempting to use the idea suggested above leads to this error:

note: inner doc comments like this (starting with `//!` or `/*!`) can only appear before items

I don't have the inclination to dig further into this at the moment. Closing this issue for another day.