Support additional RFC for casting DateTime

[Seddryck]

Accepts a string in RFC3339 / ISO8601 standard format and some variants and converts it to a DateTime.
In addition to RFC3339 / ISO8601 standard timestamps, it also accepts strings that use a space to separate the date and time as well as strings that have no explicit timezone offset.

It's potentially introducing a breaking change on how Offset is managed. The type dateTime shouldn't care about the local offset information. In version 1.x, if the offset was not specified, it was assumed to be a local time and settings of the computer regarding the offset were used. Then all the values where converted to a local time. This was an issue regarding the fundamental design principal driving this framework of being agnostic of local settings.

2020-09-08T13:42:29.190855+00:00
2020-09-08T13:42:29.190855Z
2020-09-08T13:42:29Z
2020-09-08T13:42:29.190855-05:00
2020-09-08 13:42:29.190855+00:00
2020-09-08 13:42:29.190855Z
2020-09-08 13:42:29Z
2020-09-08 13:42:29.190855-05:00