Exceptions could potentially report the exact field that raised them

Raised by @Alston-Tang in #33, all parsers would throw an exception saying where parsing failed, but the information could be better, for example:
```
    catch (const std::invalid_argument& ex)
    {
        throw parser_error("Corrupted block stat - Invalid argument", line);
```

If we could find a way to include the actual field name in the exception, that could be great.