Removed all double-quoting except for comments/echo's

Double-quoting was added in 7618da7 to allow for spaces in paths,
that was a bad idea as:

 1. most GNU Make functions can't handle spaces
 2. it breaks variable expansion on Linux/OSX e.g. ~/sketchbook
 3. Windows doesn't like double-quotes - see d5c7ed1

So basically, don't put spaces in your paths, as most Make functions
can't handle them, even if escaped, and its a bit dangerous when
shelling out to grep etc.

Single-quoting is no better either.