Automate release workflow on Windows too.

I initially hoped to have a single Makefile or script that
worked on Linux and Windows, but was unable to make it work
without massive over-complication.

So now we have makefile targets for Linux, and powershell
scripts for Windows. Documented in the README.

tweak Makefile build/upload instructions.

Fix README's link to enterprise docs

bumping version to 0.3.5

bump version to 0.3.4