message: Improve documentation for tf.strings.regex_replace
  Add more detail about the substitution mechanics and smooth out wording of op documentation.
diff: @@ -6,20 +6,30 @@ op {
  }
  in_arg {
  name: "pattern"
  - description: "The regular expression to match the input."
  + description: "The regular expression to be matched in the `input` strings."
  }
  in_arg {
  name: "rewrite"
  - description: "The rewrite to be applied to the matched expression."
  + description: <<END
  +The rewrite string to be substituted for the `pattern` expression where it is
  +matched in the `input` strings.
  +END
  }
  out_arg {
  name: "output"
  - description: "The text after applying pattern and rewrite."
  + description: "The text after applying pattern match and rewrite substitution."
  }
  attr {
  name: "replace_global"
  - description: "If True, the replacement is global, otherwise the replacement\nis done only on the first match."
  + description: <<END
  +If True, the replacement is global (that is, all matches of the `pattern` regular
  +expression in each input string are rewritten), otherwise the `rewrite`
  +substitution is only made for the first `pattern` match.
  +END
  }
  - summary: "Replaces the match of pattern in input with rewrite."
  + summary: <<END
  +Replaces matches of the `pattern` regular expression in `input` with the
  +replacement string provided in `rewrite`.
  +END
  description: "It follows the re2 syntax (https://github.com/google/re2/wiki/Syntax)"
  }
  