Update README.md
Update README.md
Merge branch 'release/v1.37.0.0-beta.6'
Initial preparations for a stand-alone build of UberPOV.

The stand-alone build is supposed to come with its own installer, and run without, or independent of, any existing official POV-Ray installation. This commit includes the following changes in preparation to this end:

  - Reviewed the `distribution` directory tree, removing a few files and updating others; most of this tree is now considered official part of UberPOV, with the exception of the help file and the icons.
  - Reviewed and updated `windows/setup.nsi`, which is now considered official part of UberPOV as well.
  - Updated Windows-specific code to use an alternate registry key and directory names to live nicely alongside with POV-Ray without mutual interference. This code can be activated via the `STANDALONE_BUILD` precompiler define.
  - The stand-alone variant will identify itself via a ".stalone" suffix after the version number.
  - Slightly modified original "piggyback" variant to more clearly identify itself in the `POV-Ray/CurrentVersion/Windows/VersionNo64` registry key.
Modified macro system to specify version, copyright and build information.

Changed distribution of macros among the files backend/povray.h and base/branch.h; added another file base/build.h specifically for stuff pertaining to an individual build, e.g. whether it's official, who compiled it, etc.
Merge branch 'stalone' into develop
preparing v1.37.0.0-beta.7
Merge branch 'release/v1.37.0.0-beta.7' into develop