Switch the preprocessor over to using the hash table library

Switch the preprocessor over to using the hash table library

Switch the preprocessor over to using the hash table library.  On my
system, this improves the runtime of the output of test/pref/macro.pl
from over 600 seconds to 7 seconds.

Macros have an odd mix of case-sensitive and case-insensitive
behaviour, plus there are matching parameters for arguments, etc.  As
a result, we use case-insensitive hash tables and use a linked list to
store all the possible isomorphs.