Log Message:
gallery-dl: Update to 1.6.3

Changes:
1.6.3
-----
- Added `metadata` post-processor to write image metadata to an external
  file (#135)
- Added option to reverse chapter order of manga extractors (#149)
- Added authentication support for `danbooru` (#151)
- Added tag metadata for `exhentai` and `hbrowse` galleries
- Improved `*reactor` extractors (#148)
- Fixed extraction issues for `nhentai` (#156), `pinterest`, `mangapark`