Implemented a modal picker view for choosing a CGFloat value

Needed to implement a picker for a floating point value, rather than perform additional validation steps off of a standard keyboard entry. As I was already utilizing your library to handle pickers in my app, I decided to implement this as a variant off of the BSModalPickerBase and to contribute my work back to your project in case you found it to be a useful offshoot.

Features:
- Accepts a maximum CGFloat value
- Works for presenting a picker for up to 3 significant figures
- Automatically adjusts the various digit selection wheels to ensure the resulting selected value does not exceed the maximum value

Cheers!