Want a component for building and tracking modal input

[ulyssa]

In order to support building iamb, I would like to have a library that helps building modal editing interfaces. To start with, I need a component that can help map keyboard input to actions to take. It needs to support the following high-level features:

• Multiple modes where input is interpreted differently, so that I can have a Normal mode, an Insert mode, and so on
• Support for prefixing input with counts (1234), registers ("A) and more
• Support for building pseudo-modes like operation-pending mode, so that common suffixes can be created for operations like d and y
• Support for handling unmapped keys so that Insert mode can just type
• Support for fetching the current mode so that the user interface can tell the user what mode they're in