Provide a better fraction implementation

[jbowtie]

When used in a cookbook, it becomes impractical to turn on the frac feature because all whole numbers are treated as numerators.

The OpenType cookbook provides a straightforward contextual version that allows for the most common and obvious usages.

http://opentypecookbook.com/common-techniques/#method-2-contextual

[DelveFonts]

@jbowtie Thank you for opening this issue. I will get this resolved at my earliest opportunity. - Delve