Fix required literal handling and add debug prints.

In particular, if we had an inner literal and were doing a case insensitive
search, then the literals are dropped because we previously only allowed
a single inner literal to have an effect. Now we allow alternations of
inner literals, but still don't quite take full advantage.

grep/Cargo.toml

@@ -14,6 +14,7 @@ keywords = ["regex", "grep", "egrep", "search", "pattern"]
 license = "Unlicense/MIT"
 
 [dependencies]
+log = "0.3"
 memchr = "0.1"
 memmap = "0.2"
 regex = "0.1.75"