Update rrdtool-release script

Update rrdtool-release script

- Update version numbers for MSVC builds too. These are defined in
  win32/rrd_config.h
- Update Copyright info and years in win32/*.rc files
- Use a variable for the current year
- Make script compatible with rrdtool major versions > 1
  (use \d instead of 1)
- Minor updates to the script considering recommendations from
  ShellCheck, e.g.:
  Use $(...) notation instead of legacy backticked `...`.