Import 'itoa' crate version 0.4.6

Bug: 163175424
Test: N/A
Change-Id: I5f3a0f346ef0c5ca8c468f69fc15afe0c2950f90
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a9d37c5
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+target
+Cargo.lock