Log Message:
converters/pandoc: Update to 3.0.1

The release note is too long to paste here. See
https://hackage.haskell.org/package/pandoc-3.0.1/changelog

As of 3.0, the pandoc package has been split into 3 packages:

  * pandoc:            Base library         (converters/hs-pandoc-base)
  * pandoc-server:     HTTP REST API        (converters/hs-pandoc-server)
  * pandoc-cli:        Command-line tool    (converters/pandoc; this package)
  * pandoc-lua-engine: Lua scripting engine (converters/hs-pandoc-lua-engine)

The original package "pandoc" no longer contains the pandoc executable, and
now it resides in "pandoc-cli". This sucks, as simply creating a new pkgsrc
package for the CLI means that converters/pandoc suddenly loses the
executable and will confuse existing users a lot. So I had no choice but to
replace the content of converters/pandoc with pandoc-cli, and synchronize
its version with converters/hs-pandoc-base.