Issues 11, 34, 35 (Date and Time fixes)

This contains:

* Addition of the precision attribute to all dates and times (including DateObjectPropertyType, etc). Please review how this was done to DateObjectPropertyType and friends, because of restrictions in how XML Schema allows you to use xs:restriction with xs:enumeration I had to make some fairly major type refactors.

* Addition of documentation indicating that it's strongly suggested to use only the appropriate condition types for CybOX patterns against dates

* Addition of documentation stating that timezone is strongly encouraged for all dates and times