Makefile refactoring and cleanup.

Add new convenience functions/macros, notably include-once, quiet,
command-v, and MKDIR.

Remove support for old-format (node-webkit 0.8 era) Win32 nwjs zips.

Move jshint configuration into standard locations and remove special
handling of it from the jshint macros.

Change file organization to separate the server, merge default settings,
simplify some other variable defaults, etc.