Meta-SECD machine
Align some instructions in makefile
Add option to provide extra flags to M4
Simplify syntax for MATCH statement

MATCH statements are now written like:

  (MATCH X (
    (... case_1 ...)
    (... case_2 ...)
    ...
    (... case_n ...)))

instead of

  (MATCH X (LIST ...))
Add comments to meta-SECD machine
Move meta-SECD machine to its own directory