0.2.0-alpha ANJARDEN SPRING

Changes:

• "pixel scanning" on canvases, shows spectrum of pixel when active
• custom cursor, pixel under cursor highlighted at high zooms
• text toggle button (currently unused)
• fixes to example plugin
• added macos.spec for pyinstaller
• archive system shows progress when loading each archive element
• Issue 1 fix (multiple tab closes when main window reinitialised)
• dynamic type determination for expr output
• can connect incompatible node outputs to inputs; indicated as red arrows
• infinite recursion in ROI nodes fix
• splash screen for Windows/Linux pyinstaller startup (not yet supported
  on MacOS pyinstaller)
• custom Datum and connection brush types now easy
• expr resizing regression fix
• multiple input buttons after load/resize fix
• status bar repaints on ui.msg, so it's updated in load and perform
• context menu on editable text caused a crash (bug in Qt). Workaround.
• comment boxes