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.
Change some heading levels and add rename doc
Add error type to package version doc
Upgrade to apm 0.73
== -> is
Upgrade to apm@0.74
Just use variable in hash
Dedupe request in apm folder

This prevents long path issues on Windows
Upgrade to apm@0.75
Don't store invalid window dimensions on Windows
Use instance method
Handle invalid serialized window dimensions
:lipstick:
:lipstick: Add space before ->
Merge pull request #2895 from atom/dh-atom-io-package-rename-doc

Change some heading levels and add docs for package renames
Merge pull request #2889 from atom/ks-windows-dimensions-on-windows

Validate window dimensions
Upgrade to language-javascript@0.34
Render the line numbers after gutter mount

Fixes #2916
Install apm in 32-bit mode on Windows CI
Upgrade to apm@0.76