Add multi-line settings and setting escapes

This is a little ugly, but the current settings format doesn't lend itself
easily to multi-line settings.  I also added new tests for this.

Examples:
```
multi_line = a
 b
\sspaces\ttabs\rcarriage\treturns\r\t = \s\t\rfoo\s\t\r
equals\=in\=name = bar
```

Results in (in Lua table format):
```Lua
multi_line = "a b"
[" spaces\ttabs\rcarriage\treturns\r\t"] = " \t\rfoo \t\r"
["equals=in=name"] = "bar"
```