In accordance with the title at line 4568, use `const&` instead of `const &`.

This allows the example to remain simple well not misleading a beginner
such a comparison is safe. Including an epsilon comparison or something
similar would overly complicate this example.
Co-authored-by: NMartin O'Shea <martin.oshea@native-instruments.com>

Added xref, massaged summary.

Changed the example so that objects are not passed by reference to other thread contexts (though threads are properly synchronized).

* Add new rule ES.3 Don't repeat yourself

* Replace function example with more inclusive/neutral language

Add a reference to topic on libraries.

Closes #1703

Closes #1705

* Update C.83 with swap for resource mgmt.

The swap is useful to implement assignments idiomatically (e.g. copy-swap idiom).

With the current enforcement, to non-virtual classes, very simple classes (e.g. `trivially_copyable`, a struct encapsulating an stl container) are suggested to have a swap. This suggestion can be argued wrong since for very simple classes copy-swap idiom is not efficient (the creation of a third object on assignment is not needed, which copy-swap does).

* Rework C.83 according to PR comments.

Also removes the only use of `decltype` in the Guidelines, FTW.

Remove string_span, recommend using `std::string_view`, `std:::span,<char>` or `gsl::span<char>` instead (#1680)

The various guidelines now have consistent Enforcements.
All C-style casts are now consistently banned, including to `(void)`.
Cast to `(void`)` should be `std::ignore =` instead.
All functional-style casts are now consistently banned,  instead of
`T(x)` use `T{x}`.

Revert "Revert "Revert "Removed gsl::string_span, recommend using std::string_view, std::span<char>, or gsl::span<char> instead"""

This reverts commit 82416094.

Revert "Revert "Removed gsl::string_span, recommend using std::string_view, std::span<char>, or gsl::span<char> instead""

This reverts commit f15ee43a.