Language features

[igagis]

1. Allow both, escaped \{, \} and unescaped {, } inside ""-string. Just for consistency with unquoted strings.
2. Do not drop explicit new-line and tab characters from ""-string?
3. Add explicit new-line char escaping in ""-strings and unquoted strings, i.e. \<new-line-char>, where <new-line-char> is the actual new-line character.