* Fixed precision calculation in DataTypeDecimalBase c-tor
* Fixed max precision calculation in getLeastSupertype
* Fixed reading past end of vector in FunctionsConversion with extractToDecimalScale
* More verbose comments on FunctionArgumentTypeValidator and validateFunctionArgumentTypes
* style and other minor fixes.
* put functions in DecimalFunctions into DecimalUtils namespace
* fixed possible buffer overflow in parseDateTimeBestEffortImpl
* fixed readDateTimeTextImpl not to require fractional part separator
(if fractional part is missing)
* Tests for code from DecimalFunctions.h
* Fixed serializing DateTime64 to string with writeDateTimeText(), fixed tests