Realtime CSG For Unity Versions Save

This release brings lots of fixes!

Fixes added by #349:

• Update Window.mat and Window.png to support proper transparency and specularity.
• Fixes from #323, where X and Z axes were transposed when creating a new box brush.
• Fixes from #355, where the undo stack is spammed with changes when dragging a material into the scene.
• Fixes from #350, where #346 had missing helper surface references, causing nullref spam.
• Fixes from #319, where rotation handles weren't showing sometimes.
• Fixes from #320, where the box transform arrows would cause zoom behavior to zoom out rapidly.
• Fixes from #354, where surface selection was unresponsive when the mouse cursor left the face of the brush. This fix also helps responsiveness of the overall tool feel better.
• Fixes from #356, where missing meta files were causing unpredictable compilation behavior, and console spam, due to the package being unwritable when added via Unity Package Manager.
• Addition from #365, which added support for invisible surface selection.
• Fixes from #366, which fixes the bottom toolbar being unresponsive if RealtimeCSG was popped out as an EditorWindow.
• Adds some new features from https://github.com/Kerfuffles/realtime-CSG-for-unity/pull/1. Please refer to the changelog there for more information.
• Adds some fixes from https://github.com/Kerfuffles/realtime-CSG-for-unity/pull/4, where static flags were not updated properly previously.

Fixes added by #370:

• Fixed corrupted materials introduced by #349, mentioned by the issue #369.

Fixes added by #371:

• Fixes #373, where RealtimeCSG would not compile on 2019.4.40f1 due to UnityEngine.Object.FindObjectsOfType() not accepting any parameters, and local static methods in InternalCSGModelManager.Lifetime.

Other msc stuff:

• 9f25003 Bumped RealtimeCSG managed version to 1.60.1.
• 181ac06 Bumped package version to reflect current RealtimeCSG managed version.

Special thanks to @Zallist and @Gawidev for the extra fixes and additions!

Changes:

• Fixes for #344

Known Issues:

• (Unity issue/Can't be fixed) RealtimeCSG cannot be fully removed without closing Unity first, due to use of native/C++ dll. A solution to this is closing Unity, and manually deleting the RealtimeCSG folder.

Changes:

• Fixes from #346

Known Issues:

• (Unity issue/Can't be fixed) RealtimeCSG cannot be fully removed without closing Unity first, due to use of native/C++ dll. A solution to this is closing Unity, and manually deleting the RealtimeCSG folder.

Changes:

• #333 RealtimeCSG can now be imported as a package using Unity Package Manager.
• #333 Icons are embedded into a generated class, which reduces clutter in the texture browser.
• #335 #340 An assembly definition was added for versions of unity that support it. Any versions older should treat RealtimeCSG as if it were a standard plugin in Plugins/
• #340 Readme updated to include information on how to import the project with supported methods, and formatting adjusted to be easier to read.
• #340 Included information on how to contribute to the project
• Included changes from #341

Known Issues:

• (Fixed by #343) Compilation error on 2020.3.13 and older, with AssetDatabase.SaveAssetIfDirty, where this API does not exist.
• (Unity issue/Can't be fixed) RealtimeCSG cannot be fully removed without closing Unity first, due to use of native/C++ dll. A solution to this is closing Unity, and manually deleting the RealtimeCSG folder.