Updated API reference docs

[nanxstats]

Fixes #167

This PR updates mkdocs.yml and the API reference docs to mirror the current codebase:

• docs/reference/rtf-document.md refreshes the entry-point description, and a new docs/reference/encoding.md documents RTFEncodingEngine/UnifiedRTFEncoder.
• docs/reference/page-layout.md now includes RTFSubline and refreshed copy for headers/footers/titles; table/text utility pages were tightened up and clarified.
• docs/reference/pagination.md covers the metadata-driven contexts, strategy registry, built-in strategies, and page feature processor.
• docs/reference/low-level.md, convert.md, assemble.md, and strwidth.md now emphasize configuration/defaults, conversion/assembly helpers, and string width with consistent mkdocstrings blocks.
• mkdocs.yml reorganized to add the encoding page, move configuration into Core, and move assembly under Utilities.

[Copilot]

Pull request overview

This PR comprehensively updates the API reference documentation to reflect the current codebase structure, reorganizing the documentation navigation and refreshing content descriptions across all reference pages.

Key changes:

• Added new encoding pipeline documentation (encoding.md) covering RTFEncodingEngine and UnifiedRTFEncoder
• Reorganized mkdocs.yml navigation to group configuration under Core and move assembly to Utilities
• Updated descriptions across all pages to be more precise and technically accurate

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
mkdocs.yml	Reorganized navigation structure: added encoding pipeline page, moved configuration to Core section, moved assembly helpers to Utilities
docs/reference/encoding.md	New page documenting encoding orchestrators for strategy-based pagination and rendering
docs/reference/text-formatting.md	Clarified descriptions of text/table attributes and reordered sections for better logical flow
docs/reference/tables.md	Updated component descriptions to emphasize spanning, grouping, and pagination features
docs/reference/strwidth.md	Focused on get_string_width function with simplified mkdocstrings configuration
docs/reference/rtf-document.md	Refreshed entry-point description to emphasize unified encoding pipeline
docs/reference/pagination.md	Expanded coverage to include contexts, strategy registry, built-in strategies, and page feature processor
docs/reference/page-layout.md	Added RTFSubline component and clarified header/footer/title descriptions
docs/reference/low-level.md	Retitled to "Core utilities" and added RTFDefaults documentation
docs/reference/convert.md	Simplified to focus on LibreOfficeConverter with cleaner mkdocstrings block
docs/reference/assemble.md	Changed to document each assembly function with individual mkdocstrings blocks

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