borrow code from Marpa test suite to get started
external lexing (EL): convert operator literals to L0 rules: t+
external lexing (EL): finished convert operator literals to L0 rules: t+
EL: lexeme/token split: t+
non-LE, but nice: make another test file pass: t+
LE: token sorting longest possible to shortest possible
LE: token sorted longest possible to shortest possible: t+
LE: avoid comment stripping in the external lexer: t+
LE: strip comment in the external lexer: t+
LE: touchup: t+
LE read() lexes fact code
LE: add lexer test
LE: fact() parsed ok with external lexer
LE: touchups on external lexer
LE: 15 of 23 LTS files pass
LE: 16 of 23 LTS files pass