Split EBML module into a reader and a writer module

Minor refactoring, no review.

Closes #2739

Author: catamorphism

src/librustc/metadata/csearch.rs

@@ -1,6 +1,7 @@
 // Searching for information from the cstore
 
 use std::ebml;
+use Reader = std::ebml::Reader;
 use syntax::ast;
 use syntax::ast_util;
 use syntax::ast_map;
@@ -181,7 +182,7 @@ fn get_field_type(tcx: ty::ctxt, class_id: ast::def_id,
                   def: ast::def_id) -> ty::ty_param_bounds_and_ty {
     let cstore = tcx.cstore;
     let cdata = cstore::get_crate_data(cstore, class_id.crate);
-    let all_items = ebml::get_doc(ebml::Doc(cdata.data), tag_items);
+    let all_items = Reader::get_doc(Reader::Doc(cdata.data), tag_items);
     debug!("Looking up %?", class_id);
     let class_doc = expect(tcx.diag,
                            decoder::maybe_find_item(class_id.node, all_items),