Add an autosuggest widget: autosuggest-execute.

[hitripod]

(Originally PR #122, retarget it to features/execute_widget branch.)

Add back autosuggest-execute-suggestion from #61 which is removed after rewriting.

[ericfreese]

Thanks @hitripod. I want to play with this a little bit myself before releasing, and will probably release this with v0.3.0. Would be great if we could add tests as well. Take a look at scripts/test.zsh for examples of how we're testing the other widgets, and send another PR if/when you get some tests in. Otherwise, I'll probably write some tests for this new widget at some point before releasing v0.3.0.

[hitripod]

Thank you, too. I would love to do that :)

[Cottser]

Just wanted to say thanks for this! I was looking for this functionality (just started using zsh-autosuggestions) and appreciate that this is back. I've added the widget code with a different function name to my ~/.zshrc temporarily until v0.3.0 is released.