Consider making `macro_table` precede `symbol_table`

[popematt]

#353 (comment)

Macros are declared after symbols.

Is there a specific reason for this ordering? Food for thought: if symbols were declared after macros, would that make it clearer that the symbols defined in an encoding directive are not yet available for use in the macro definitions in that same encoding directive?

I am unaware of any specific reasoning for having the symbol table come before the macro table. We should see if there are any other pros/cons to switching the order, and decide whether to make the change.