Trace dependencies in build

Openscad has an option:

       -d file.deps
              If the -d option is given, all files accessed while exporting are written to the given  deps  file  in
              the syntax of a Makefile.

This can be used by Make to properly trace dependencies and figure out when re-builds are necessary and when not. Additionally it may make sense to use Ninja as it's more designed for the style of build we are currently doing, i.e. generating a makefile from a script. It does require users to install Ninja which may be less common than Make (but it does have small statically linked executables available to download for all platforms).