pos: a library for positive numbers

Pos is designed to work with nonempty containers and also with configuration where zero is invalid.

Includes the following features:

• a type Pos for representing positive numbers, excluding zero
• presets for commonly used positive values such as _1P, _2P, _3P, ...
• arithmetic operations
• functions for safely converting to and from Pos

Where Pos is used:

• The cybus package uses the Pos type with multidimensional arrays and indices where each dimension of the array is nonzero and the number of dimensions is nonzero.
• Pos is also used in the primus package for dealing with nonempty containers.

Additional notes:

• The Num instance is excluded to limit potential runtime errors arising from the use of fromIntegral, subtraction, or negation.
• The Num1 class in the primus package offers a safer alternative to Num since it respects inherent bounds for those number types. Instances for Natural, Word, Pos, Int, etc. are defined.