--User changes

-Support 4k monitors, and in general, properly scale any monitor that is not HD.
 -Allow for a spatial filter of radius zero, which means do not use a spatial filter.
 -Add new variations: concentric, cpow3, helicoid, helix, rand_cubes, sphereblur.
 -Use a new method for computing elliptic which is more precise. Developed by Discord user Claude.
 -Remove the 8 variation per xform limitation on the GPU.
 -Allow for loading the last flame file on startup, rather than randoms.
 -Use two different default quality values in the interactive renderer, one each for CPU and GPU.
 -Creating linked xforms was using non-standard behavior. Make it match Apo and also support creating multiple linked xforms at once.

--Bug fixes
 -No variations in an xform used to have the same behavior as a single linear variation with weight 1. While sensible, this breaks backward compatibility. No variations now sets the output point to zeroes.
 -Prevent crashing the program when adjusting a value on the main window while a final render is in progress.
 -The xaos table was inverted.

--Code changes
 -Convert projects to Visual Studio 2017.
 -Change bad vals from +- 1e10 to +-1e20.
 -Reintroduce the symmetry tag in xforms for legacy support in programs that do not use color_speed.
 -Compiler will not let us use default values in templated member functions anymore.

openexr.cmd

@@ -15,7 +15,7 @@ if not exist ".\output" mkdir .\output
 
 cd IlmBase
 
-cmake -G "Visual Studio 14 2015 Win64"^
+cmake -G "Visual Studio 15 2017 Win64"^
       -DCMAKE_PREFIX_PATH="%current%\output"^
       -DCMAKE_INSTALL_PREFIX="%current%\output"^
       .\
@@ -24,7 +24,7 @@ cmake --build . --target install --config Release -- /maxcpucount:8
 
 cd ..\OpenEXR
 
-cmake -G "Visual Studio 14 2015 Win64"^
+cmake -G "Visual Studio 15 2017 Win64"^
       -DCMAKE_PREFIX_PATH="%current%\output"^
       -DCMAKE_INSTALL_PREFIX="%current%\output"^
       -DILMBASE_PACKAGE_PREFIX="%current%\output" ^