Add rolling stream method

[benmccann]

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Description

This adds a rolling stream(n) method which allows us to do many different operations such as forEach, map, filter, anyMatch, allMatch, etc. on rolling groups of rows. rollWithRows(Consumer<Row[]> rows, int n) is the same as stream(n).forEach(consumer), so I've deprecated it since it's the same thing, but less powerful

@ryancerf depending on which PR is merged first (i.e. this one or #579) either you or I might need to rebase to put this method on Relation

Testing

Existing unit tests cover this functionality. They're effective too because they caught a bug in my initial implementation.

[benmccann]

What do you think about the name? Would rollingStream(n) be better than stream(n)?

[lwhite1]

This adds a rolling stream(n) method which allows us to do many different operations such as forEach, map, filter, anyMatch, allMatch, etc. on rolling groups of rows. rollWithRows(Consumer<Row[]> rows, int n) is the same as stream(n).forEach(consumer), so I've deprecated it since it's the same thing, but less powerful

There is so much awesome stuff getting done now. It's really exciting.

What do you think about the name? Would rollingStream(n) be better than stream(n)?

So long as you're rolling (i.e. moving forward one row at a time as in a rolling average), I think rollingStream is preferable. I often, also, find it useful to step forward by groups of n rows. We may want to support that option. Or is that built in here as well? If you can do either with this implementation I prefer stream().

[lwhite1]

Other than my one in-line comment and the replies to the PR, I think this is great. So much more powerful than what we have.

[ryancerf]

This looks good to me, but I would like to discuss the possibility of supporting analytic functions. See #582. Analytic functions would provide similar rolling stream support.

[benmccann]

I renamed to rollingStream and added a steppingStream as well