Instaloader

- Many fixes related to error handling (26, 32. 29, 31)
- `--only-if` option to filter posts (motivated by 15, 24)
- Options `--no-captions` and `--no-geotags` (25)
- Download videos in Sidecars (41)
- Remove command line option `--shorter-output`
- Rename `--skip-videos` to `-no-videos`
- New documentation: https://instaloader.readthedocs.io/
- Major refactorings and code cleanups

Bugfix release - Added proper handling of HTTP error code 429 which occurs if too many requests are made in a certain time. Their occurrence was reported in 29. Instaloader now tries to wait if necessary to avoid reaching Instagrams rate limits.
Additionally, some other minor bugfixes and enhancements are made concerning 26, 30 and 32.

Bugfix release - Improved error handling to alleviate 26. If a file cannot be downloaded within three attempts, the file is skipped without aborting the whole target (hashtag/profile).

Bugfix release - fixes AttributeError exception when invoked without being logged in.

- Download user stories (target `:stories` and options `--stories` and `--stories-only`) contributed by e5150 in 28
- Retry get requests for downloading pictures (26)
- Download own private profile (27)
- Minor fixes and enhancements

- Options `--dirname-pattern` and `--filename-pattern` added (21, 22, 23)
- Fixed `download_feed_pics()`
- Minor fixes and enhancements