Implement star-normal-form rewriting.

* src/ltlvisit/snf.cc, src/ltlvisit/snf.hh: New files.
* src/ltlvisit/Makefile.am: Distribute them.
* src/ltlvisit/simplify.cc, src/ltlvisit/simplify.hh: Call snf(f) for
all f[*].
* src/ltltest/reduccmp.test: Test it.
* doc/tl/tl.tex, doc/tl/tl.bib: Document it.

src/ltltest/reduccmp.test

@@ -291,6 +291,11 @@ for x in ../reduccmp ../reductaustr; do
      run 0 $x '{{a;b*;c}&{d;e*}&{f*;g}&{h*}} <>-> x' \
               '{{f*;g}&{h*}&{{a&&d};{e* & {b*;c}}}} <>-> x'
      run 0 $x '{a&b&c*}|->!Xb' '{(a&&b)|((a&&b):c*)}|-> X!b'
+     run 0 $x '{a;(b*;c*;([*0]+{d;e}))*}!' '{a;{b|c|{d;e}}*}!'
+     # not reduced
+     run 0 $x '{a;(b[*2..4];c*;([*0]+{d;e}))*}!' \
+              '{a;(b[*2..4];c*;([*0]+{d;e}))*}!'
+     run 0 $x '{((a*;b)+[*0])[*4..6]}!' '{((a*;b))[*0..6]}!'
      ;;
   esac