makes the login experience a bit friendlier to non-developer users

was broken in #82

closes #79

fixes relative URL resolution (closes #78) by relying on new IndieAuth\Client package.

likes and reposts the tweet on twitter first, then sends a syndication URL in the micropub endpoint

let's give this a shot

closes #71

* new route `/edit?url=` intended to be used as an edit button target, which detects the type of post and redirects to the appropriate editing interface
* implemented the edit interface for favorites

closes #69

update to "create" scope by default, but allow the user to choose "post" as a fallback. also updates indieauth/client to 0.2 for json support.

closes #67

* adds setting to choose the property to use for the syndication targets
* all existing users default to the old value `syndicate-to`
* new users default to `mp-syndicate-to`

closes #66

allows backdating and future-dating posts