Remove ambiguity between ISO 8601 reference and UTC requirement in time request parameters

[kaestli]

The current standard document says:

All time values are specified in UTC and should use one particular variation of the ISO 8601 standard
with the addition of sub-seconds:
YYYY-MM-DDTHH:MM:SS.ssssss
[...]
YYYY-MM-DDTHH:MM:SS
[...]
YYYY-MM-DD

This is kind of a contradiction, as ISO 8401 says on time strings with no time zone indicated:
If no UTC relation information is given with a time representation, the time is assumed to be in local time.

In order to avoid this, I'd like to propose to remove the reference to ISO 8601 from the text. The patterns and the requirement of those to be in UTC are a sufficient definition of the request parameters.

[crotwell]

+1 on clarifying this.

I would prefer that web services be required to accept the Z for time zone. So these formats would be acceptable too:

YYYY-MM-DDTHH:MM:SS.ssssssZ
YYYY-MM-DDTHH:MM:SSZ

Related somewhat to this inside stationxml: FDSN/StationXML#105

In general, I am in favor of appending a "Z" to all times to make the timezone explicit.