rustc: Rename rustc_macro to proc_macro

This commit blanket renames the `rustc_macro` infrastructure to `proc_macro`,
which reflects the general consensus of #35900. A follow up PR to Cargo will be
required to purge the `rustc-macro` name as well.

src/libproc_macro_plugin/parse.rs

@@ -0,0 +1,26 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Parsing utilities for writing procedural macros.
+
+extern crate syntax;
+
+use syntax::parse::{ParseSess, filemap_to_tts};
+use syntax::tokenstream::TokenStream;
+
+/// Map a string to tts, using a made-up filename. For example, `lex(15)` will return a
+/// TokenStream containing the literal 15.
+pub fn lex(source_str: &str) -> TokenStream {
+    let ps = ParseSess::new();
+    TokenStream::from_tts(filemap_to_tts(&ps,
+                                         ps.codemap().new_filemap("procmacro_lex".to_string(),
+                                                                  None,
+                                                                  source_str.to_owned())))
+}