emaps-describe-keymap-bindings: Add support for multiple keymaps

[GuiltyDolphin]

Being able to describe multiple keymaps at once would be nice, though likely only through direct calls ((keymap &rest keymaps)).

It'd probably be fine just to display one keymap after the other (textually).

• Possible future feature: allow collapsing/expanding keymaps.

[GuiltyDolphin]

Here's a thought on why this might be useful.

Say you wanted to view all the keymaps active for your current major/minor mode combination - it might be handy to be able to run a function (e.g., emaps-describe-keymap-bindings-current-major-minor-mode) then have it bring up a buffer with a list of (collapsible) keymaps for the current major and minor modes. Each of these would have a view similar to what would display with emaps-describe-keymap-bindings.

Note on describe-bindings

Format

describe-bindings provides a buffer with the following format:

Key translations:
key             binding
---             -------

...

^L
`X-minor-mode' Minor Mode Bindings:
key             binding
---             -------

...

^L
`Y-minor-mode' Minor Mode Bindings:
key             binding
---             -------

...

^L
Major Mode Bindings:
key             binding
---             -------

...

^L
Global Bindings:
key             binding
---             -------

...

^L
Function key map translations:
key             binding
---             -------

...

^L
Input decoding map translations:
key             binding
---             -------

...

[back]

(Where ^L is the literal character)

It seems the format of each section is therefore:

Title:
key             binding
---             -------

...

Spacing

There are newlines between some sets of bindings (within sections), I believe this is done by longest common prefix.

Displays even for empty/non-existent keymaps

describe-bindings seems to display sections for minor modes that have empty/non-existent keymaps. For example, there is a section for auto-complete-mode:

^L
`auto-complete-mode' Minor Mode Bindings:
key             binding
---             -------

Which is empty, and there is no keymap for auto-complete-mode.