Allow looping over ranges

[bsilvia]

Fixes #60

Some design considerations:

• It is not possible to specify negative numbers e.g. foreach (var i in -10..0) due to limitations with the implicit creation of Index from Range
• The range is inclusive of the end so foreach(var i in 0..10) will yield [0, 1, ..., 10] which is equivalent to for(var i = 0; i <= 10; i++)
• Since the end is inclusive, a range where the start and end are equal will yield 1 value e.g. foreach (var i in 0..0) will iterate once with i == 0

[ardalis]

Thanks!

If you want, can you add example(s) to the Usage section in the README?

[bsilvia]

I'd be happy to add examples. Are you referring to #62?