This updates the Trojan Source code safety checker to take arguments to

turn off Unicode confusable checks as a whole, or to disable them for

specific Unicode aliases.
To allow this to work, the build-confusables.py script now provides a

mapping of confusable alias names to numeric indexes, and a reverse of

that map. The number indexes are then referenced in the confusable

character map. The checker can then use this to quickly determine which

alias a particular character is part of, and to then exclude that if

provided in the call.
There's no user-level customization at this stage. This is purely an

update to the safety checker code. Additional work is still needed to

allow customization of these settings and to provide it at all the right

stages of diff generation.
There's also a fix that was encountered when posting this change, which

caused a crash when Python failed to identify the name of a Unicode

character.

Unit tests pass on all supported versions of Python.
Tested this along with in-progress changes to allow customization of

which confusables are checked.