Adding the datatypes HSVColor and DateTime.

[oliveirarleo]

Adding the datatypes HSVColor and DateTime.

The type DateTime is added according to the ISO 8601
The type HSVColor is added according to the HSL Format
resolves #76

[barbieri]

thanks, let's see what @gunnarx and @Floix think

[barbieri]

@oliveirarleo please add tests/model/test_contants.py covering them

[SebastianSchildt]

If theres is consensus to merge I will not block, but I feel this is the "most wrong" way to add units. We create a randomly curated list of "allowed" units, some of which are in VSS and some not, and probably the first thing everybody needs to to, once he uses vSS besides the standard catalogue is hacking in more units in his fork (which I already did, and which also ultimately leads to this PR)

Anyway, my thoughts on this are here already: #76 (comment)

[danielwilms]

@barbieri: create an issue

• for datatypes and
• a second one for units (< how to deal with additional units curated list or not)
• list possible datatypes as start to be more "future proof"

@danielwilms: create issue for units mismatch code vs. docs

[barbieri]

@danielwilms created #89 and #91 as requested. Since you did not create the issue on the units mismatch, I did that as #90.

[danielwilms]

@barbieri That's generous ;) thanks a lot!

[danielwilms]

@gunnarx, please close the PR

[gunnarx]

Refer to tickets for more info.