Revert Majority to conj=False
Add p => q, and s ? d1 : d0 to expression parsing

The '=>' operator is a symbolic Implies, and is right-associative
The ?: operator is a symbolic ITE, and is right-associative
Add <=> equivalence to expr parsing
Add Majority to expr top matter
Add OneHot0, OneHot, and Majority functions

The expression parser can now handle all the operators in the expr.py
module.