Create Env task

[splatteredbits]

Create an Env task. It should have one Variables property whose members are the variables to create/edit/update. Each variable's value can be a string, in which case the task sets that variable to that value, or a map. If a map, the variable being edited is assumed to be a list (with values separated by [IO.Path]::PathSeparator ) and values to prepend to the list, append to the list, or removed from the list would be given by Prepend, Append, and Remove properties, respectively. Users could use the Separator property to change the default separator. An empty string is allowed, in which case the value is just added to the beginning or end of the value.

- Env:
    Variables:
        SomeVar: SomeValue
        Path:
            Prepend: VALUE
            Append: VALUE
            Remove: VALUE
            Separator: VALUE