Trigger changeQuery event when user inputs something into the search field

[SanderKleykens]

Description

This closes #944 by triggering a changeQuery event as soon as the user inputs something into the search field.

Types of changes

• Chore (tooling change or documentation change)
• Refactor (non-breaking change which maintains existing functionality)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[mtriff]

This looks like a great addition, but right now it won't function as intended. A changeQuery event will be fired every time a key is pressed, even if it doesn't actually change the query (i.e. arrow keys, delete/backspace keys when the query box is empty, etc.). I think you want to hook into the input event instead. We aren't doing that already, so you'll need to add an _onInput method to Choices.

Please also rebase on the latest version of the master branch.

[mtriff]

Let's also add a check to ensure that changeQuery is fired before the search event. You can see an example of firing the search event here.

[Xon]

#1166 implements an _onInput event handler and only triggers a search event if the search has run on new input basically resulting it being identical to this changeQuery functionality.

What I've just added is a search even which gives an empty search string (and result count of 0) when search has finished.