Sopel-github

Fixed:
* Comments containing blank lines would cause errors (43)

Added:
* Handling for several new event types:
* Pull request reviews (20)
* Pull request assignments (23)
* Pull request labels (23)
* Pull request milestones (35)
* Issue & pull request title edits (36)
* Releases (21)
* Handling of draft pull requests (34)
* Handling for draft pull requests marked ready for review (34)
* Converting `:emoji:` to Unicode emoji in most text output (17)
* Requires optional dependency: https://pypi.org/project/emoji/

Changed:
* `secret` setting is now called `client_secret` (42)
* The plugin will automatically migrate configs to use the new name, but
manual editing is encouraged in advanced setups (e.g. if the user Sopel
runs as cannot write to the config file)
* Quoted text is ignored when generating comment output (41)
* Unicode ellipsis now used instead of three periods (31)
* Oxford comma now used in generated lists (40)
* Webhook payload processing is handed off to a separate thread (22)
* Bottle can handle only one request at a time; doing this should minimize
the potential for failed deliveries, as GitHub's webhook delivery service
times out very quickly

Fixed:
* GitHub URL regexes should match all possible usernames & repo names (38)
* Of particular note: dots (`.`) are now recognized in repository links,
such as Sopel's website repo: https://github.com/sopel-irc/sopel.chat

Fixed:
* Error with empty issue/PR description or commit message (39)

Changed:
* Webhook now says "merged" instead of "closed" for merged PRs (18)
* Re-opened issues/PRs will also trigger the webhook now (27)

Fixed:
* Webhook ignores issue, PR, and review comments that were edited (16, 24)
* Commit summary correctly says "1 file" instead of "1 files" (37)
* Some webhook output grammar fixed (15)
* Handle comments submitted via email correctly WRT line-endings (30)
* Replace uses of long-deprecated `SopelMemory` method (33)

Fixed:
* Refactoring unintentionally broke registering new repo webhooks (14)

Meta:
* PyPI package description should be rendered to HTML now (fixed content-type)

Changed:
* "GitHub" is now properly capitalized everywhere in text output (9)
* Usage output uses `help_prefix` from config instead of hardcoded `.` (12)

Fixed:
* git.io shortening was cutting off GET parameters of input links. (11)