Merge pull request #1 from limetext/master

Update to latest commit
First try to use Buffer.addObserver().
Revert "First try to use Buffer.addObserver()."

This reverts commit 7838beebe315345aa4712de14efc7d32655bebd2.
Simplifies selection callback
Providing view instead of selection to GetSelectionMessage()
Adds a fastest algorithm when moving cursor (WIP)
Fixes a bug when moving backward
Adds a TODO
Merge pull request #431 from emersion/master

frontend/html: cursor improvements