Love poem generator

[lemonsaurus]

A command that uses Markov to generate a poem.

@martmists already started working on this, but the PR was closed for inactivity in https://github.com/python-discord/seasonalbot/pull/97. Marty said he might have time to look at this some more in 4 weeks, so I'm assigning this ticket to him so we can get this finished at that time.

Here's what remains to be done with this:

• [ ] Fix all of the outstanding review comments left by @scragly on https://github.com/python-discord/seasonalbot/pull/97
• [ ] Remove Shakespeare corpus
• [ ] Instead, use work from the following authors: John Keats, William Wordsworth, Lord Byron, William Blake, Rabby Burnes, Walter Scott.

[melodicht]

Hi, I am interested in working on this.