Feature: show line numbers and/or context in diffs

[epage]

@colin-kiegel from assert-rs/assert_cli#17

Just a random idea. :-)

git diffs provide some context and line numbers. If the output is really huge and lines are similar, this might be helpful - but certainly not straightforward. Should probably even be implement upstream first in the difference crate.

@@ -93,7 +93,7 @@
 #[derive(Debug)]
 pub struct Assert {
     cmd: Vec<String>,
-    expect_success: bool,
+    expect_success: Option<bool>,
     expect_exit_code: Option<i32>,
     expect_stdout: Option<OutputAssertion>,
     expect_stderr: Option<OutputAssertion>,

instead of

-    expect_success: bool,
+    expect_success: Option<bool>,

[epage]

This is blocked on #7