fix escapes in string literals, support JS-style escapes

Backslashes in strings were causing infinite loops.

This commit replaces string literal parsing with a technique using regexes and JSON.parse to interpret the escape sequences.
use proper escaping in stringified string literals

Use JSON.stringify's ability to make nice double-quoted strings.

With tests for parse/stringify.
Merge pull request #203 from meteor/strings

Fix handling of escapes in string literals