add brainfuck->tree-il compiler

add brainfuck->tree-il compiler

* module/Makefile.am (BRAINFUCK_LANG_SOURCES): Compile at the end. Add
  compile-tree-il.scm.

* module/language/brainfuck/compile-tree-il.scm: New compiler, compiles
  to tree-il instead of scheme. I thought it would be more illustrative,
  though there are some uncommented bits.

* module/language/brainfuck/parse.scm: Modify not to put a header on the
  scheme representation. After all, we don't put <scheme> before scheme
  code, do we? :)

* module/language/brainfuck/spec.scm: Add tree-il compiler.

* module/language/tree-il.scm: Understand (set! (lexical foo) ...).

* module/system/base/language.scm: Update license. Actually, updates
  licenses on all these.