[sharesix] Add new extractor
[moevideo] Add new extractor
Merge pull request #3691 from naglis/moevideo

[moevideo] Add new extractor
[moevideo] Add videochart.net to _VALID_URL
Merge pull request #3690 from naglis/sharesix

[sharesix] Add new extractor
[moevideo] Make filesize exact
[khanacademy] Improve _VALID_URL (Closes #3695)