Simplenote

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* Actually remove the since support like I thought I had. I could have
re-implemented since in as per tags so it filters after pulling everything
else, but since (ha!) I used "since" for a faster note loading there seems
little point.

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* Documentation updatess only

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* Update to the Simperium API: https://simperium.com/docs/http/
* Breaking changes:
* The since parameter has been removed. Simperium supports the since parameter, but as a cursor, not a date.
* The syncnum key no longer exists (this is an upstream change)
* Things seem to be UTF-8 by default
* This should largely be a drop in replacement though: E.g. Simperium uses id instead of key, but simplenote.py handles that for you.

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* Sort tags in get_note and update_note

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* Unescape html entites due to api change

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* Bug fix for an error introduce as a result of code review improvements.