Updated some of the callbacks in callback.lua.

Update get.lua to use the new callbacks.
The old "code" module is now the "mime" module.
Updated all modules that depended on it.
Updated url.lua to use the new namespace scheme, and moved the
    escape and unescape functions that used to be in the code.lua module
    to it, since these are specific to urls.
Updated the callback entries in the manual.

src/mime.lua

@@ -0,0 +1,104 @@
+-- make sure LuaSocket is loaded
+if not LUASOCKET_LIBNAME then error('module requires LuaSocket') end
+-- get LuaSocket namespace
+local socket = _G[LUASOCKET_LIBNAME] 
+if not socket then error('module requires LuaSocket') end
+-- create code namespace inside LuaSocket namespace
+local mime = socket.mime or {}
+socket.mime = mime
+-- make all module globals fall into mime namespace
+setmetatable(mime, { __index = _G })
+setfenv(1, mime)
+
+base64 = {}
+qprint = {}
+
+function base64.encode()
+    local unfinished = ""
+    return function(chunk)
+        local done
+        done, unfinished = b64(unfinished, chunk)
+        return done
+    end
+end
+
+function base64.decode()
+    local unfinished = ""
+    return function(chunk)
+        local done
+        done, unfinished = unb64(unfinished, chunk)
+        return done
+    end
+end
+
+function qprint.encode(mode)
+    mode = (mode == "binary") and "=0D=0A" or "\13\10" 
+    local unfinished = ""
+    return function(chunk)
+        local done
+        done, unfinished = qp(unfinished, chunk, mode)
+        return done
+    end
+end
+
+function qprint.decode()
+    local unfinished = ""
+    return function(chunk)
+        local done
+        done, unfinished = unqp(unfinished, chunk)
+        return done
+    end
+end
+
+function split(length, marker)
+    length = length or 76
+    local left = length
+    return function(chunk)
+        local done
+        done, left = fmt(chunk, length, left, marker)
+        return done
+    end
+end
+
+function qprint.split(length)
+    length = length or 76
+    local left = length
+    return function(chunk)
+        local done
+        done, left = qpfmt(chunk, length, left)
+        return done
+    end
+end
+
+function canonic(marker)
+    local unfinished = ""
+    return function(chunk)
+        local done
+        done, unfinished = eol(unfinished, chunk, marker)
+        return done
+    end
+end
+
+function chain(...)
+    local layers = table.getn(arg)
+    return function (chunk)
+        if not chunk then
+            local parts = {}
+            for i = 1, layers do
+                for j = i, layers do
+                    chunk = arg[j](chunk)
+                end
+                table.insert(parts, chunk)
+                chunk = nil
+            end
+            return table.concat(parts)
+        else
+            for j = 1, layers do
+                chunk = arg[j](chunk)
+            end
+            return chunk
+        end
+    end
+end
+
+return code