Docs: improvements for "references - phpdoc - tags - version"
Docs: improvements for "references - phpdoc - tags - version"

Summary:
* Made a hybrid of the current text in PSR-19 and the original text.

Syntax:
* Replaced "vector" with "Semantic Version" as per PSR 19.

Description:
* Combined existing text with the current description in PSR-19.

Examples:
* Added more VCS examples, as per PSR 19.

Other:
* Minor inline markup and grammar fixes.
* Made the syntax outline a code block.
* Collected external links at the bottom of the document.

Ref: https://github.com/php-fig/fig-standards/blob/master/proposed/phpdoc-tags.md#518-version

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