Use lexical-binding in tests and fix crash exposed

argdesc in byte-code function objects may be an integer rather than a
list, so handle that case gracefully.

Choose the default symbol more intelligently

Fixes Wilfred#163
Closes Wilfred#245

Particular thanks to @matzebond for the first implementation of this
feature!

Add bookmark support

Fixes Wilfred#203

Always autoload callables if they aren't loaded

Fixes Wilfred#117

Pretty-print primitive values

As of 1d2954b we pretty-print keymaps and hooks by default, but this
broke display of variables of other types. Fix that.

Add a note in the changelog for 0de7c15

Rename file to avoid confusion with other projects' unit tests

Add n and p as movement keybindings

We might want to use TAB in future for other things, perhaps
expanding/collapsing headings.

Mention when manual links were implemented

This was done in 2053fd4.

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