Add support for a list of files or embeds

[clari7744]

Rationale

Allows easy sending of multiple embeds in one message without using ctx.send, same way as single embed works. Same thing with files.

Summary of changes made

I added a check to see if result is an Iterable and if it's all Embeds or Files, and if so it sends all of those. However, it checks for discord.py 2+ for multiple embeds.

Checklist

• [x] This PR changes the jishaku module/cog codebase
  • [x] These changes add new functionality to the module/cog
  • [ ] These changes fix an issue or bug in the module/cog
  • [ ] I have tested that these changes work on a production bot codebase
  • [ ] I have tested these changes against the CI/CD test suite
  • [ ] I have updated the documentation to reflect these changes
• [ ] This PR changes the CI/CD test suite
  • [ ] I have tested my suite changes are well-formed (all tests can be discovered)
  • [ ] These changes adjust existing test cases
  • [ ] These changes add new test cases
• [ ] This PR changes prose (such as the documentation, README or other Markdown/RST documents)
  • [ ] I have proofread my changes for grammar and spelling issues
  • [ ] I have tested that any changes regarding Markdown/RST syntax result in a well formed document

[scarletcafe]

I don't really like this because this both causes eager iteration of returned iterables, and could cause jishaku to block the event loop if the iterable takes time to traverse, or never ends.

[scarletcafe]

I've decided that this is probably best not to do, considering the possible side effects. I recommend either yielding the File/Embeds as you go or using ctx.send directly if you want to bundle them into the same message.