non-functional progress

... still not grokking Rust lifetimes and borrowing ...

Getting these errors:

   Compiling jmh-diff v0.1.0 (file:/Users/benjchristensen/development/github/jmh-diff)
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:40:23: 40:27 error: `line` does not live long enough
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:40         .map(|line| { line.as_slice().split(' ') }) // TODO this doesn't compile
                                                                                        ^~~~
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:37:5: 46:11 note: reference must be valid for the method call at 37:4...
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:37     file.lines()
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:38         .map(|line| { line.unwrap() })
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:39         .filter(|line| { !line.as_slice().starts_with("Benchmark") })
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:40         .map(|line| { line.as_slice().split(' ') }) // TODO this doesn't compile
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:41         .fold(map, |map, columns| {
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:42             let key = (columns.nth(0), columns.nth(1)); // TODO this doesn't compile
                                                                  ...
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:40:21: 40:51 note: ...but borrowed value is only valid for the block at 40:20
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:40         .map(|line| { line.as_slice().split(' ') }) // TODO this doesn't compile
                                                                                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:42:24: 42:31 error: cannot borrow immutable argument `columns` as mutable
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:42             let key = (columns.nth(0), columns.nth(1)); // TODO this doesn't compile
                                                                                         ^~~~~~~
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:42:40: 42:47 error: cannot borrow immutable argument `columns` as mutable
/Users/benjchristensen/development/github/jmh-diff/src/main.rs:42             let key = (columns.nth(0), columns.nth(1)); // TODO this doesn't compile