Feature request: Expand snippets with shortcuts

#### Description of the problem / feature request / question:
I've tried to figure out if this feature already exists, but I can't find anyone mentioning it.
I think it would be extremely useful to have an auto-expander/text-expander/text-replace feature in Lepton.

Examples of other tools implementing it:
Alfred: https://www.alfredapp.com/help/features/snippets/#expansion
Dash: https://kapeli.com/dash_guide#snippets
Text expander: https://textexpander.com/
But they are all complex proprietary tools with tons of other features that I have no need for.

I think this feature would work extremely well with Lepton, and it seems like no other open source snippet manager does this.