Improvements for argtable2

[Removed by request]

I'm using Ubuntu 12.10 dev with libargtable2-dev 12-1. I have some suggestion to improve argtable2:

1. argtable2 allows filling up the variable in the related struct before arg_parse to assign a default value. There could be an argument for this in the arg_***n functions to allow a default value. This would reduce a code line for every command line option which wants to use a default value.

2. The numeric arg_***n functions could have 2 arguments for the minimum and maximum value which is allowed for the related command line options.

3. Maybe arg_intn could be arg_longn to allow a wider range of numbers without creating an own function. It would be usefull too if it would be possible to define for all arg_***n functions if they are a signed or unsigned datatype.