Adds default value and getInt and getFloat method.

This pull request to add those features:
1. add getInt to get value as an Integer or NaN if value is not a number,
2. add getFloat method to get value as a float or NaN if value is not a number,
3. add default value to get, getInt and getFloat to be able to give a default value if key is not found.

I hope this will be accepted.

JM.