Add a new Criteria constructor for creating sequence

[jslee02]

Problem

No convenient way to create a sequence Linkage.

Solution

Add an utility constructor to Linkage::Criteria to create a sequence Linkage:

Criteria(BodyNode* start, BodyNode* target, bool includeBoth = false);

Issues

• Resolve Allow Chain to include bodies have multiple children #1268

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[mxgrey]

I realize that this is just copying from Chain.hpp and that I'm probably the one that came up with the includeBoth concept, but I'm not actually sure that I understand the motive. Why should the options be:

1. Include both the start and the target, or
2. Leave out whichever one is upstream

I don't really see what the significance of the upstream link would be that we would want to leave it out. The only thing I can think of is maybe we want to "start" from a body node that's at a fork and then "target" a body node that's at the end of a branch. I suppose that would be helpful for constructing chains within multi-arm skeletons.

I'm fine with leaving it as it is and merging it, but I thought I'd go ahead and voice my own confusion at an API that I probably made myself. If anyone else finds it confusing, we should probably consider tweaking it somehow.

[jslee02]

I realize that this is just copying from Chain.hpp

For the record, it is identical except that mChain option is false in this constructor. That's why I didn't make Chain use this constructor (maybe I should let Chain just use this constructor and change the option to true?).

Regarding includeBoth, I assumed that this option is about whether it includes the parent joint of the upstream body or not because the joint is technically not in between start and target bodies. In this case, we could change the option name and the document more clear.

[mxgrey]

Oh good call! You're exactly right: it's about whether to include the parent joints of both the start and the target. A more descriptive name would definitely be helpful. Maybe includeUpstreamParentJoint?