remove :as support from use expressions

The `:as` keyword in use statements really just confuses the meaning of
`use` and `require` make some interactions surprising. By removing this
`use` always behaves exactly as expected.

doc/language.rst

@@ -335,8 +335,7 @@ we might want to do.
 
      (use (string :exclude (substr/4 join/2)
                   :joxify
-                  :rename ((sub-word/3 str-subword) (join/2 str-join)
-                  :as str)))
+                  :rename ((sub-word/3 str-subword) (join/2 str-join))))
 
 Lets break this down into actions.
 
@@ -360,9 +359,6 @@ Lets break this down into actions.
    imports being carried forward. *NOTE* note the joxification of
    `sub-word/3`. Since we specified `joxify` earlier we must must
    refer to it as `sub-word/3` instead of `sub_word/3`.
-5) As. This has the exact as in `require` in that it provides an alias
-   for the namespace name specified. This allows you to refer to any
-   function in that namespace with the alias.
 
 Functions
 ---------

examples/complex_module.jxa

@@ -3,8 +3,7 @@
     (attr sfoo 123)
     (use (lists :only (member/2 append/2)
                 :rename ((member/2 mbr))))
-    (use (file :as f
-               :exclude (delete/1)
+    (use (file :exclude (delete/1)
                :rename ((change_group/2 chgrp)
                         (change_mode/2 chmod))))
     (attr super_duper "Hello World")

examples/sieve-of-eratosthenes.jxa

@@ -1,6 +1,6 @@
 (ns sieve-of-eratosthenes
     (require lists io)
-    (use (joxa.core :as core :only (!=/2))
+    (use (joxa.core :only (!=/2))
          (erlang :only (rem/2 +/2))))
 
 (defn sieve (v primes)
@@ -13,4 +13,3 @@
 
 (defn+ sieve (v)
   (sieve (lists/seq 2 v) 1))
-