Improvements to OUR-CVFH Estimation, including mapping from clusters to features and doc fixes

Fixes #737 by adding a `vector<short> cluster_axes_` to `OURCVFHEstimation`. This protected field consists of a count of the number of signatures that have been computed per cluster. It is set by `computeRFAndShapeDistribution` at the same time as `compute`'s output. When all axes are properly disambiguated, it will consist only of the value 1 (one entry per cluster). When some cluster i has multiple SGURF solutions, instead of 1, the vector will contain the number of SGURFs in location i.

Also fixes a typo in the documentation and another in the warning (plural of axis is axes, so "both axes" not "both axis").
Space is not permitted in macro definitions, but it is okay to put it when a macro is called.

Generally, our policy is not to fix space issues in lines we don't touch with updates, and do fix in lines we touch. In this case the line in question is being updated anyways, so it would be nice to fix the space as well.