Add support for `rustdoc` shorthand link syntax & deps bump

[virtualritz]

Implemented recognition and processing of shorthand [`code`] patterns. These patterns are now properly handled for both link stripping and docs.rs link generation.

Changes:

• Add detection of shorthand patterns like [function] in documentation.
• Support stripping brackets from such patterns when using --intralinks-strip-links flag.
• Generate proper docs.rs links for recognized shorthand patterns.
• Bumped deps, small cargo_metadata update-related fix (sep. commit).

Used e.g. just now in dithereens README.md generated from shorthand links in its lib.rs.

[virtualritz]

Fixed a bug in my impl. I've been using my fork w/o (other) issues now since Sep. 9, when I submitted this PR originally. I also added tests for this feature.

[geeknoid]

@orium I'd love to see this PR merged