FIX:
Previously, running any plugin command other than Settings or About
    would cause Notepad++ to crash if the user had multiple selections.
    This commit would fix this issue by, whenever they use a single-selection-only command,
    informing the user and bailing out early if they have multiple selections.
FEAT:
Add a new after-build to NPPJSONViewer.vcxproj
    that creates an NPPJSONViewer plugin directory (if one doesn't already exist)
    in the appropriate Notepad++ installation (%ProgramFiles%\Notepad++ for an x64 build or %ProgramFiles(x86)%\Notepad++ for a Win32 build)
    and then copies the NPPJSONViewer.dll that you just built into that plugin folder.
I also tried to add another action that would run that Notepad++ installation afterwards,
    but I couldn't figure out how to do that.