fix macOS build (following Projucer changes made in Windows, which removed /Applications/JUCE/modules from its headers). move JUCE headers under source control, so that Windows and macOS can both build against same version of JUCE. remove AUv3 target (I think it's an iOS thing, so it will never work with this macOS fluidsynth dylib).

modules/juce_graphics/image_formats/jpglib/changes to libjpeg for JUCE.txt

@@ -0,0 +1,16 @@
+
+I've included libjpeg in the JUCE tree because loading jpegs is a pretty useful thing to
+be able to do, but I've left out as many files as possible to keep it lean-and-mean.
+
+If you want to get hold of the full version of libjpeg, it's freely available at:
+
+http://www.ijg.org/
+
+
+Please note that part of the IJG's license for libjpeg states that:
+
+  "If you use it in a program, you must acknowledge somewhere in 
+   your documentation that you've used the IJG code".
+
+..so if you release a JUCE program that reads JPEGs, you should probably give them a mention.
+