Add Vim modelines

Change-Id: I23f30cd9be56089498089f8b12abe3f3e186b525
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/argument.cpp b/argument.cpp
index 42abd99..d89764d 100644
--- a/argument.cpp
+++ b/argument.cpp
@@ -76,3 +76,5 @@
 
 const std::string ArgumentParser::true_string = "true";
 const std::string ArgumentParser::empty_string = "";
+
+// vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4