Add code for analyzing dependencies between syntaxes

And also to generate independent SyntaxSets. This will later be used
to improve bat startup time.

src/lib.rs

@@ -40,6 +40,7 @@ mod preprocessor;
 mod pretty_printer;
 pub(crate) mod printer;
 pub mod style;
+mod syntax_dependencies;
 pub(crate) mod syntax_mapping;
 mod terminal;
 pub(crate) mod wrapping;