Introcude some more typed wrappers: setBranch, setAlias, setStage

[m1rm]

In my company, we use set('branch',...) and set('stage', ...) quite frequently. In addition I noticed that there is no "setAlias" function for a host so far.

I'd be happy to implement setters and getters, if you think it is useful.

[antonmedv]

i guess ok for setBranch,

but definitely no for setAlias