[$] Development tools: Sashiko, b4 review, and API specification

The kernel project has a unique approach to tooling that avoids manycommonly used development systems that do not fit the community's scale andways of working. Another way of looking at the situation is that the kernelproject has often under-invested in tooling, and sometimes seems bent ondoing things the hard way. In recent times, though, the amount of effortthat has gone into development tools for the kernel has increased, withsome interesting results. Recent developments in this area include theSashiko code-review system, a patch-review manager built into b4, and a newattempt at a framework for the specification and verification of kernelAPIs.