[Feature Request] default tag support for slices

[GrigoriyMikhalkin]

Currently default tag is unsupported on slices. As it explained here:

The default tag is unsupported on slices because slice parsing uses , as the separator, as does the envconfig tags separator.

What I propose is to change default tag to support following format:

default=value1;value2;etc

If this value will be applied to slice, it will be split by ;. If applied to string, value is applied as is. Else, it will panic. I would gladly implement this feature.

[vrischmann]

Hi,

I guess that could work yes. I'd be happy to review your PR.