Migrate docs and GitHub templates to Markdown

[PtPrashantTripathi]

Fixes # by migrating RST docs and misplaced GitHub templates to Markdown

Changes proposed in this pull request:

• Converted README.rst → README.md and CHANGES.rst → CHANGELOG.md
  (RST-specific syntax replaced with equivalent Markdown)
• Moved PULL_REQUEST_TEMPLATE.md and ISSUE_TEMPLATE.md from the repo
  root into .github/ — GitHub only auto-applies these templates when
  they live in that directory
• Updated setup.py to read README.md + CHANGELOG.md for
  long_description (was already declaring text/markdown content type
  while reading .rst files — now consistent)
• Updated MANIFEST.in to include CHANGELOG.md instead of CHANGES.rst

Status

• READY
• HOLD
• WIP (Work-In-Progress)

How to verify this change

• Open a new PR or issue — the templates should auto-populate
• python setup.py --long-description should render clean Markdown
• README.md and CHANGELOG.md render correctly on the GitHub repo page