Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

vendor/backtrace/examples/backtrace.rs

@@ -0,0 +1,5 @@
+use backtrace::Backtrace;
+
+fn main() {
+    println!("{:?}", Backtrace::new());
+}

vendor/backtrace/examples/raw.rs

@@ -0,0 +1,52 @@
+fn main() {
+    foo();
+}
+
+fn foo() {
+    bar()
+}
+fn bar() {
+    baz()
+}
+fn baz() {
+    print()
+}
+
+#[cfg(target_pointer_width = "32")]
+const HEX_WIDTH: usize = 10;
+#[cfg(target_pointer_width = "64")]
+const HEX_WIDTH: usize = 20;
+
+fn print() {
+    let mut cnt = 0;
+    backtrace::trace(|frame| {
+        let ip = frame.ip();
+        print!("frame #{:<2} - {:#02$x}", cnt, ip as usize, HEX_WIDTH);
+        cnt += 1;
+
+        let mut resolved = false;
+        backtrace::resolve(frame.ip(), |symbol| {
+            if !resolved {
+                resolved = true;
+            } else {
+                print!("{}", vec![" "; 7 + 2 + 3 + HEX_WIDTH].join(""));
+            }
+
+            if let Some(name) = symbol.name() {
+                print!(" - {}", name);
+            } else {
+                print!(" - <unknown>");
+            }
+            if let Some(file) = symbol.filename() {
+                if let Some(l) = symbol.lineno() {
+                    print!("\n{:13}{:4$}@ {}:{}", "", "", file.display(), l, HEX_WIDTH);
+                }
+            }
+            println!("");
+        });
+        if !resolved {
+            println!(" - <no info>");
+        }
+        true // keep going
+    });
+}