documentation for dateTime/formatString should comply with stds and good practice

[mobb]

Documentation for dateTime formatStrings needs review and update. It should
a) promote existing standards (ISO 8601),
b) acknowledge common general practices

Examples should be justified, and dropped if they cannot be. one example needing close examination is the use of "Ws" to denote parts of month names.

[mobb]

The EDI date-time check working group will address this

[mbjones]

Related to issue #248.