[PSR-5] enhancements

[jaapio]

This pull request introduces enhancements to the PHPDoc specification (proposed/phpdoc.md) by refining tag handling and adding support for inline tags. The most important changes include updates to the ABNF definition for tags, the introduction of inline tags, and the addition of tag specialization for improved metadata organization.

Enhancements to tag handling:

• Updated the ABNF definition to modify the syntax for tag-specialization and tag:

  • tag-specialization now excludes the - character, and tag syntax includes an optional specialization prefix followed by a hyphen.

• Added the concept of tag specialization (5.3.1 Tag Specialization) to provide a scoped context for tags. Specialized tags can differ from the standard catalog, and parsers may ignore unsupported specialized tags.

Support for inline tags:

• Introduced inline tags (5.2.1 Inline tags) within descriptions. Inline tags must start with {@ and end with }. Escaping is supported for closing braces using {}. Inline tags are limited to regular tags and do not apply to annotation tags.

Structural refinements:

• Updated the table of contents to reflect the addition of inline tags and the reorganization of tag-related sections.

Minor Adjustments:

Updated recommendations for formatting in summaries and descriptions, such as discouraging formatting in summaries and clarifying Markdown usage in descriptions.