Move validate command into doc fragment and fix a few typos

lib/ansible/modules/files/replace.py

@@ -27,6 +27,7 @@ DOCUMENTATION = """
 module: replace
 author: "Evan Kaufman (@EvanK)"
 extends_documentation_fragment: files
+extends_documentation_fragment: validate
 short_description: Replace all instances of a particular string in a
                    file using a back-referenced regular expression.
 description:
@@ -61,12 +62,6 @@ options:
     description:
       - Create a backup file including the timestamp information so you can
         get the original file back if you somehow clobbered it incorrectly.
-  validate:
-    required: false
-    description:
-      - validation to run before copying into place
-    required: false
-    default: None
   others:
     description:
       - All arguments accepted by the M(file) module also work here.