Add tx builder set recipients

[waterst0ne]

Description

I just started working on #168 which enables the tx_builder to add a list of recipients instead of iterating over the add_recipient method multiple times.

• The set_recipients() method replaces the precedent list and overwrites it with the new one.
• You can always use add_recipient() to append to the list.

Notes to the reviewers

Checklists

All Submissions:

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

New Features:

• I've added tests for the new feature
• I've added docs for the new feature
• I've updated CHANGELOG.md

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[thunderbiscuit]

Overall just a few small things. But the biggest question is whether we should introduce the breaking change that would have add_recipient() use the AddressAmount type.

[notmandatory]

@waterst0ne oops, it looks like you force pushed an old version somehow. If you need help fixing it back up let me know.

[notmandatory]

ACK 8703803

[notmandatory]

@thunderbiscuit have your requested changes been addressed? if so you'll need to add an approve before we can merge.

[thunderbiscuit]

ACK 8703803.