Rebuild SimpleBook mw2pdf When Any of its Sources Are Changed

Now that mw2pdf has migrated to TypeScript, there is a build process that must take place after every source code edit for the changes to go live. 

Unless we automatically trigger this rebuild, the developer will have to take an extra step during testing. 

Let's add tooling to the devenv so that mw2pdf is automatically rebuilt every time that a source file is changed.