Improve literate mode.

* Expect a blank line as delimiter between text and code (#2821).
* Don't change indentation of code. It is not necessary and leads to
  erroneous locationData. (#2835)
* Don't modify blank lines and reverse the change in the lexer.
* Don't ignore indentation with mixed whitespace.
Test case for literal mode: Code blocks must be preceded by blank line.
Compiled JavaScript files for improved literal mode.
Merge pull request #2838 from marchaefner/master

Improve literal mode.