This means that a HySymbol remembers its original name. That is, `a-b` and `a_b` are different symbols although `(setv a-b 1)` and `(setv a_b 1)` set the same variable (namely, `a_b`).
Most of the edits in this commit are to switch underscores to hyphens in places where mangling hasn't happened yet.
I removed some lexer tests since the lexer no longer does any mangling.
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