add support for portfolio data (closes #169)

[johnlaing]

No description provided.

[eddelbuettel]

Looks great. Only minor question (or suggestion): should it be getPortfolio() for consistence as it is a getter? Or not because bds, bdp, bdh, ... are shorthand?

[johnlaing]

I don't have a preference either way. Happy to change if you'd like.

[eddelbuettel]

As a user (and author) I do prefer getFoo() for various foo, so if you're up for a search+replace I think it makes it easier. But as I said, here we do have counter examples -- and if the Bloomberg documentation refers to 'portfolio' as a function ... So your call.

[johnlaing]

I'll change it. I like bdp/bds/bdh for their simplicity, but there are others like getTicks. I suppose this is more similar to the latter.