Really small whitespace changes in generated code.
Makes it easier to use and remember, and makes the variable `module/*headerpath*` make more sense.
Don't pull in a global header <janet/janet.h> unless we need to.
This should speed up start time and reduce malloc/free usage to about 15% of what is what previously for startup. The current cost is slightly larger binary as the representaion of the image is currently less compact than source code.
