New implementation of auto save (#58):

saves:

* on editor blur (including split switch)
* on switching files (goto UI etc.)
* on window close
Update, now with `File:Save` command and configurable saveTimeout.
Change saveTimeout to 2s, update whitespace stripper to "change".
Fix undefined exception for sessions like zed::start
Merge pull request #296 from zedapp/new-auto-save

New implementation of auto save