Update default Slider min and max

[marcofugaro]

when passing only a value to the Slider like State.Slider(10), now:

• if the slider value is between 0 and 1, the max is 0 and the min is 1
• otherwise the max (min if it's negative) it's the double of the value

Closes #3

[marcofugaro]

Wow! What honor! Thank you! 😄