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
Fix typo
Merge pull request #2904 from maschs/ms-fixTypo

Fix typo
Upgrade to apm 0.72
Map ctrl-f4 to core:close command on Windows

Closes #2903
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