documentation (#1200)

- reintroduce documentation internal links
- remove `gsl::` prefix in table so it is the same as in the other tables
- fix documentation for span::element_type

Co-authored-by: Werner Henze <w.henze@avm.de>

README.md

@@ -74,12 +74,12 @@ u32string_span                     | ☐   | Deprecated. An alias to `basic
 cu32string_span                    | ☐   | Deprecated. An alias to `basic_string_span` with a char type of `const char32_t`
 
 ## The following features have been adopted by WG21. They are deprecated in GSL.
-Feature                            | Deprecated Since | Notes
------------------------------------|------------------|------
-gsl::unique_ptr                    | C++11            | Use std::unique_ptr instead.
-gsl::shared_ptr                    | C++11            | Use std::shared_ptr instead.
-gsl::byte                          | C++17            | Use std::byte instead.
-gsl:joining_thread                 | C++20 (Note: Not yet implemented in GSL) | Use std::jthread instead.
+Feature                                                           | Deprecated Since | Notes
+------------------------------------------------------------------|------------------|------
+[unique_ptr](docs/headers.md#user-content-H-pointers-unique_ptr)  | C++11            | Use std::unique_ptr instead.
+[shared_ptr](docs/headers.md#user-content-H-pointers-shared_ptr)  | C++11            | Use std::shared_ptr instead.
+[byte](docs/headers.md#user-content-H-byte-byte)                  | C++17            | Use std::byte instead.
+joining_thread                                                    | C++20 (Note: Not yet implemented in GSL) | Use std::jthread instead.
 
 This is based on [CppCoreGuidelines semi-specification](/~https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#gsl-guidelines-support-library).
 

docs/headers.md

@@ -230,7 +230,7 @@ See [F.23: Use a `not_null<T>` to indicate that “null” is not a valid value]
 using element_type = T;
 ```
 
-The type of the pointed-to object.
+The type of the pointer or smart pointer that is managed by this object.
 
 #### Member functions