Log Message:
gallery-dl: Update to 1.12.1

Changes:
### Additions
- [4chan] add extractor for entire boards (#510)
- [realbooru] add extractors for pools, posts, and tag searches (#514)
- [instagram] implement a `videos` option (#521)
- [vsco] implement a `videos` option
- [postprocessor:metadata] implement a `bypost` option for downloading the
  metadata of an entire post (#511)

### Changes
- [reddit] change the default value for `comments` to `0`
- [vsco] improve image resolutions
- make filesystem-related errors during file downloads non-fatal (#512)

### Fixes
- [foolslide] add fallback for chapter data extraction
- [instagram] ignore errors during post-page extraction
- [patreon] avoid errors when fetching user info (#508)
- [patreon] improve URL pattern for single posts
- [reddit] fix errors with `t1` submissions
- [vsco] fix user profile extraction … again
- [weibo] handle unavailable/deleted statuses
- [downloader:http] improve rate limit handling
- retain trailing zeroes in Cloudflare challenge answers