Avoid unnecessary escape sequences inside string literals

[gflohr]

Feature request.

Input:

const foo = 'bar\tbaz';

Output:

const foo='bar\tbaz';

Expected:

const foo='bar baz';

Well, the expected output outsmarts the GitHub editor. The space should really be a tab character.

Rationale: The escape sequence \t is two bytes long, the literal tab just one, and there is never a need to escape it withing string literals.

The same goes for \v, '\r', '\f', '\b', although theses characters are, of course, much less common.