Add stability message for Atom.io API

This indicates that the Atom.io API is not frozen - this is describing the state
of things, not announcing a new policy.
Move gutter member into a showLineNumbers observe block
Prepare 0.115
Upgrade to tree-view@0.109.0
Merge pull request #2920 from atom/bo-gutter-toggle-api

Move gutter member into a showLineNumbers observe block
Merge pull request #2760 from atom/package-api-stability-notice

Add stability message for Atom.io API
Upgrade to markdown-preview@0.91
Upgrade to markdown-preview@0.92
Update git-diff to fix atom/git-diff#31
Upgrade to markdown-preview@0.93
Prepare 0.116
:memo: Add missing :
Add spec for loading theme with incomplete variable file
Add cssForFile to LessCompileCache
Load packages with the fallback variables
Load fallback variables in the user’s stylesheet
import the fallback variables in the base theme
Use less-cache@0.13.0
Upgrade to tabs to fix tab size issue
Don’t need the absolute path, just `variables` 

`static` is already on the path