Collapsible sidebar items

[allan2]

The sidebar can make it hard to find information if there are many enum variants or methods.

For example, a user interested in finding trait implementations for isocountry::CountryCode may look for this info in the sidebar. To do so, the user would have to tediously scroll through all of the variants and methods first.

Current

Proposed

Proposed changelog:

• .sidebar-title heading moved from center to left, with left padding of 10px
• .sidebar-links > a padding changed from 10px to 15px
• collapsible link added to right side of .sidebar-title
• collapsible link uses the styling of .collapse-toggle (colour of #999, typographic styling on the plus/minus character)
• adjusted margins and vertical border (no double border) for adjacent collapsed items

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The collapsing UX can also be improved for the main content section, but I will put that in a separate issue.

If you like this idea for the sidebar, I'd be happy to submit a PR.

[GuillaumeGomez]

The bars are a step back and something we voluntarily removed a while back. I think being able to collapse sidebar sections is a good idea tough.

[allan2]

What are you referring to when you say bars?

[GuillaumeGomez]

"borders" around Variants, Methods, Trait Implementations.