Performance benchmarking suite

[lsf37]

In the early days JFlex used to have a performance benchmarking suite, in particular to compare to JLex and to figure out the trade-offs for different scanning engine options (pack/table/switch etc).

It bit-rotted fairly quickly and never even made it into the public repo. It would be nice to write such a benchmarking suite again to get better information on speed/memory trade-offs like #697, #199, or #196.