Add a StringLiteral class as a replacement for JavaWriter.StringLiteral.  Advantages include:
  * References differentiate between String and StringLiteral
  * StringLiteral.toString() still allows to be directly passed to String.format, et. al.
  * You can get the value back after the literal has been passed around.
Merge pull request #61 from gk5885/string-literal

Add a StringLiteral class as a replacement for JavaWriter.StringLiteral