Add "Trim Whitespace" to the sandbox.
Rip out Trim Trailing Space.
Break out of callback hell.
Use an object to avoid global state.
Merge branch 'master' into trim_whitespace
Drop sessionbeforesave eventbus.
Don't delete newlines at end of file if cursor is there.
Create a presave handler for the sandbox.
Fix Makefile filenames.

According to the documentation:

https://www.gnu.org/software/make/manual/html_node/Makefile-Names.html
Fix Configuration:Preferences:Toggle Trim Whitespace On Save.
Cleanup handler toggling logic.
Presave not guaranteed to happen before saving.
Push Configuration:Preferences:Toggle Trim Whitespace On Save into Sandbox.
Abort if preference not set.
Use config.togglePreference everywhere.
Merge pull request #120 from robru/patch-3

Fix Makefile filenames.
Fixes #123 by adding "internal" flag to commands (both core and custom
sandbox commands), also adds `Window:Close` command.
Merge branch 'master' into trim_whitespace
Extremely common window-closing shortcut.
Merge pull request #124 from robru/patch-4

Extremely common window-closing shortcut.