Improve support of parsing ISO 8601 date and time strings

[joachimmetz]

Improve support of parsing ISO 8601 date and time strings.

https://en.wikipedia.org/wiki/ISO_8601#Times

[Onager]

This includes adding support for fractional time components.

[joachimmetz]

@Onager not entirely clear what you mean based on your comment, but based on the plaso issue that was referenced I think the functionality you want has been added in 40ca0a0