dotnetexe: Use DOTNETFRAMEWORK_Exec()
make: Add MAKE_PID
system: SYSTEM_TMPDIR -> SYSTEM_TEMPDIR
dotnet, dotnetassembly: Simplify by working against dotfiles
Add tempdir module providing a global Makery temp directory
Add nuget module for fetching and unpacking NuGet packages
Add nugetassembly module for using assemblies from NuGet packages