rollup merge of #19224: frewsxcv/unprefix-json-types

Addressing the issues brought up in [this thread](https://github.com/rust-lang/rust/pull/19114#discussion_r20614461)

This pull request:

* Unpublicizes reexports
* Renames type aliases:
 * `json::JsonArray` ☞ `json::Array`
 * `json::JsonObject` ☞ `json::Object`

src/test/run-pass/issue-2804.rs

@@ -21,7 +21,7 @@ enum object {
     int_value(i64),
 }
 
-fn lookup(table: json::JsonObject, key: String, default: String) -> String
+fn lookup(table: json::Object, key: String, default: String) -> String
 {
     match table.find(&key.to_string()) {
         option::Some(&json::String(ref s)) => {