The .rst generation doesn't escape the trailing `_` and the docs build
gets upset due to using `type` as a reference target then.
For the better or worse, revert to using tpe. Though I acknowledge this
means we need to be careful with trailing underscores because our docs
build is so fragile.
Partly reverts b9eabbabba.
* All "Broxygen" usages have been replaced in
code, documentation, filenames, etc.
* Sphinx roles/directives like ":bro:see" are now ":zeek:see"
* The "--broxygen" command-line option is now "--zeexygen"
