re-work last few chapters

Now that "Advanced type systems" is pretty much only two things, merging
the lifetimes chapter, which is very short, into it makes a lot of
sense.

In addition, we kinda wanted to see if we could fit another project in
here anyway, so let's do this and then it makes room!

Author: steveklabnik

src/SUMMARY.md

@@ -88,9 +88,9 @@
 
 - [Patterns](ch18-00-patterns.md) (perhaps an appendix?)
 
-- [More Lifetimes](ch19-00-more-lifetimes.md) (perhaps merge this into advanced type system features?)
+- [Advanced Features](ch19-00-advanced-features.md)
 
-- [Advanced Type System Features](ch20-00-advanced-types.md) (perhaps called "Advanced Traits"?)
+- [Un-named project](ch20-00-unnamed-project.md)
 
 - [Appendix](appendix-00.md)
     - [Keywords](appendix-01-keywords.md)

src/ch20-00-advanced-types.md renamed to src/ch19-00-advanced-features.md

@@ -33,6 +33,18 @@ You have to write unsafe code to FFI
 
 ### Unsafe Traits
 
+## More Lifetimes
+
+### Lifetimes that depend on other lifetimes
+
+'a: 'b stuff: subtyping
+
+### Higher ranked trait bounds
+
+for<'a>
+
+Needed for closures
+
 ## Associated Types
 
 More common than the other things, less common than the rest of the book

src/ch19-00-more-lifetimes.md

@@ -0,0 +1 @@
+# Un-named project