Added docs for `fmt`
Document `htmlEscape`
Document `inNull` and `join`
Document `mean`.
Document `notAmong`
Document `notEqual` and `notMatch`
Document `product`
Document `promise`
Document `quotient`
Document `safeString`
Document `sumBy`
Document `sum`.
Merge pull request #85 from cibernox/master

Finish documenting all macros