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.

test/httptest.lua

@@ -5,14 +5,14 @@
 -- needs "AllowOverride AuthConfig" on /home/c/diego/tec/luasocket/test/auth
 dofile("noglobals.lua")
 
-local host, proxyh, proxyp, request, response
+local host, proxyhost, proxyport, request, response
 local ignore, expect, index, prefix, cgiprefix
 
 local t = socket.time()
 
 host = host or "diego.princeton.edu"
-proxyh = proxyh or "localhost"
-proxyp = proxyp or 3128
+proxyhost = proxyhost or "localhost"
+proxyport = proxyport or 3128
 prefix = prefix or "/luasocket-test"
 cgiprefix = cgiprefix or "/luasocket-test-cgi"
 
@@ -129,8 +129,8 @@ request = {
 	method = "POST",
 	body = index,
     headers = { ["content-length"] = string.len(index) },
-    port = proxyp,
-    host = proxyh
+    proxyport = proxyport,
+    proxyhost = proxyhost
 }
 expect = {
 	body = index,
@@ -170,8 +170,8 @@ check_request(request, expect, ignore)
 io.write("testing proxy with redirection: ")
 request = {
 	url = "http://" .. host .. prefix,
-    host = proxyh,
-    port = proxyp
+    proxyhost = proxyhost,
+    proxyport = proxyport
 }
 expect = {
 	body = index,
@@ -267,7 +267,7 @@ io.write("testing manual basic auth: ")
 request = {
 	url = "http://" .. host .. prefix .. "/auth/index.html",
 	headers = {
-		authorization = "Basic " .. (socket.code.b64("luasocket:password"))
+		authorization = "Basic " .. (socket.mime.b64("luasocket:password"))
 	}
 }
 expect = {