The currently suggested vim modeline formatting string to allow .livemd
files to render as markdown on GitHub works, but confuses vim itself.
```
<!-- vim: syntax=markdown -->
```
When opening a .livemd file with the suggested modeline in vim it errors
when it tries to parse `-->` as a modeline option.
e.g.
```
"2021/day2.livemd" 81L, 1616B
Error detected while processing modelines:
line 1:
E518: Unknown option: -->
```
The fix is to replace the suggested vim modeline
```
<!-- vim: syntax=markdown -->
```
With a modeline declaration format that indicates when the modeline
options are complete, allowing vim to ignore the rest of the line.
```
<!-- vim: set syntax=markdown: -->
```
Reference
- vim issue: https://github.com/vim/vim/issues/1648
- especially this comment: https://github.com/vim/vim/issues/1648#issuecomment-296386153Fixes#773
* Improve file select layout on long paths
* Automatically back up notebooks without a file
* Run formatter
* Add margin when there are no sections
* Add an informative note about autosave directory
* Store autosave path instead of file in the config
* Rename autosave dir to autosave path
* Fix insert mode escape on section headlines
* Show ellipsis on selected file too
* Always create the default directory
* Apply review comments
* Add support for Mix runtime as a default
* Support default runtime options in the CLI
* Set cell status to queued while runtime is being started
* Clean up tests
* Add explore page
* Move sidebar to a configurable component
* Fix homepage test
* Add images
* Store example notebooks in files and make explore notebooks linkable
* Fix tests
* Raise on invalid notebook slug
* Keep just the file contents in notebook info
* Move notebook lookup to Explore
* Exclude notebooks in progress
* Add embedded runtime for evaluating code in the Livebook VM
* Update lib/livebook_web/live/session_live/embedded_live.ex
Co-authored-by: José Valim <jose.valim@dashbit.co>
* Use standard error proxy globally in the Livebook node
* Add configuration env variable for setting the default runtime
* Increase evaluation response assertion timeouts
Co-authored-by: José Valim <jose.valim@dashbit.co>
