linux/Dockerfile : use default -O1 instead of -O2.

Update linux Dockerfile to use cabal new-build.

linux/Dockerfile - use resolver lts-12.12.

Use released pandoc-citeproc, texmath.

Makefile: Fix executable path in trypandoc target.

Bump to 2.2.3.2, update man page, changelog.

Bump to 2.2.3.1, update man page and changelog.

Update README.md.

Make sure pandoc-windows-*.msi are deleted as intermediate files.

Minor cabal file changes.

Requested by 'stack upload.'
Different format for minimum cabal version.
Use of autogen-modules.