Add reader-oriented GTF guides and API reference (3.0.1)

[iskandr]

Installation and a complete parsing example now share the home page. Guides start with filtering and writing annotations; v3 migration and progress details follow. Public APIs are rendered from source, with the same typography and expanded sidebar used by PyEnsembl and mhctools.

Correct the existing gene-expression example to key by gene identity, and repair malformed return docstrings that prevented a strict API build. Add a strict documentation workflow and internal-link/anchor checks. Merge current master and bump 3.0.2 → 3.0.3. The stacked follow-up #95 uses 3.0.4.

Validation: ./lint.sh, ./test.sh (213 passed), ./docs.sh (7 pages, 138 internal links) and 3 executed examples. Checks use generated HTML and example execution; the user requested no browser.

Closes #86. Closes #92.

[coveralls]

Coverage Report for CI Build 38447892648

Coverage remained the same at 97.236%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• 4 coverage regressions across 1 file.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

4 previously-covered lines in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
create_missing_features.py	4	88.89%

---

Coverage Stats

Relevant Lines:	398
Covered Lines:	387
Line Coverage:	97.24%
Coverage Strength:	6.77 hits per line

---

💛 - Coveralls