Improve handling of fields which begin with a numeral

[ChimeraCoder]

Just discovered this quirk:

If a JSON object contains the field "3ED", it will be translated to the unexported field _ED. If the object contains both "3ED" and "4ED", both will be translated to unexported fields named _ED (which will fail to compile with the error message duplicate field _ED).

[sarathsp06]

This looks fixed , @ChimeraCoder please do confirm that or revert