Many changes for adding dynamic (fiber-level) scope.

- Allow passing a table to fibers, which make fiber level scope easier.
- Add fiber/getenv, fiber/setenv, dyn, and setdyn
- Remove meta, *env*, and *doc-width*
- Some functions changed dignatures, and no longer take an env

examples/3sum.janet

@@ -14,5 +14,5 @@
   (map keys (keys solutions)))
 
 (def arr @[2 4 1 3 8 7 -3 -1 12 -5 -8])
-(print "3sum of " (string/pretty arr) ":")
-(print (string/pretty (sum3 arr)))
+(printf "3sum of %P: " arr)
+(printf "%P\n" (sum3 arr))