[recipes.py] Move fetch, lint and bundle parsers to separate modules.

recipe_engine/fetch.py

Index: recipe_engine/fetch.py
diff --git a/recipe_engine/fetch.py b/recipe_engine/fetch.py
index 2dd80cd81ddd4260d870765dca9e968237202b5d..4a44109fed291c16a9606285f3afc7a4a663b531 100644
--- a/recipe_engine/fetch.py
+++ b/recipe_engine/fetch.py
@@ -592,3 +592,20 @@ class GitilesBackend(Backend):
       rev_json.message_lines,
       spec,
       has_interesting_changes(spec, rev_json.changed_files))
+
+
+def add_subparser(parser):
+  fetch_p = parser.add_parser(
+    'fetch',
+    description='Fetch and update dependencies.')
+
+  def postprocess_func(parser, args):
+    if args.no_fetch:
+      parser.error('--no-fetch doesn\'t make sense with fetch command')
+
+  fetch_p.set_defaults(
+    command='fetch',
+    # fetch action is implied by recipes.py
+    func=(lambda package_deps, engine_flags: 0),
+    postprocess_func=postprocess_func,
+  )