Noveldown

Bug fixes
- all: specify a user agent to dodge anti-scraping tools (fixes WanderingInn)
- all: use smarter exponential backoff that accounts for HTTP timeouts (fixes WanderingInn)

Bug fixes

- Added support for the new *The Wandering Inn* website
- Added rate limiting to all sources (exponential backoff) to avoid hammering source servers

Feature changes

- Added **asynchronous downloading** - expect a 4-10x speed improvement depending on your internet connection!
- *The Wandering Inn* is now also also aliased to "TWI"
- Custom paths now have to be specified as an argument rather than an option (`noveldown TWI <path>` instead of `noveldown TWI --path <path>`)
- `noveldown -s` is now an alias of `noveldown --supported-ids`
- New source: **Pale by Wildbow**!

Bug fixes

- WanderingInn: Extra "<< Previous chapter" and "Next chapter >>" are now dropped from the final EPUB

Feature changes
- Removed `get` subcommand in the CLI
- i.e., instead of `noveldown get <URL>`, use `noveldown <URL>`

- Fixed debug statements spamming the console when downloading "A Practical Guide to Evil" (7edd5e6fd0297843bfc5b60d59728c9139f17074)
- Fixed crashing when downloading "A Practical Guide to Evil" (823f3e5968738740ea016310caa29636266efee5)
- Fixed incorrect chapter count when downloading "A Practical Guide to Evil" (38ac7aded5e7d1b76dd4ca91811ecaa8785e63e2)
- Added the URL of the source webnovel to the "Publisher" field

Initial release!