Consider support for reST (reStructuredText) preview

[gagath]

• Gitea version (or commit ref): 1.1.2
• Git version: N/A
• Operating system: Debian Stretch
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant
• Log gist: N/A

Description

I have a lot of README files formatted in reStructuredText but the README rendered can only render Markdown files. Please consider reStructuredText rendering for those of us who prefer reST rather than Markdown.

I do not know how this can be done however, maybe by calling external Python library if there is no reST library in Go.

Screenshots

[lunny]

duplicated with #374

[lunny]

see #2564