Wrap algorithms in <div algorithm> to generate variable references (#1529)

* Wrap algorithms in <div algorithm> to generate variable references

With this change, it is possible to click on a variable and see all its
uses highlighted within the algorithm scope, and to be warned about
missing definitions / unused variables.

https://speced.github.io/bikeshed/#var-and-algorithms

* Fix missing/erroneous/unused variables

Author: apasel422