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

tools/bars.janet

@@ -49,7 +49,7 @@
   # Make ast from forms
   (def ast ~(fn [&opt params] (default params @{}) (,buffer ,;forms)))
 
-  (def ctor (compile ast *env* source))
+  (def ctor (compile ast (fiber/getenv (fiber/current)) source))
   (if-not (function? ctor)
     (error (string "could not compile template")))
   (ctor))