Add vector package support

Use the exprtk::rtl::vecops::package<double> package so that expressions
can make use of vectors.

Vectors may be useful when needing to sort a list of sensors, for
example.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I0e63e2f9803e81d45e25efd119df5bb885066351
diff --git a/virtualSensor.cpp b/virtualSensor.cpp
index ce429f6..25c127c 100644
--- a/virtualSensor.cpp
+++ b/virtualSensor.cpp
@@ -154,6 +154,7 @@
     }
 
     symbols.add_constants();
+    symbols.add_package(vecopsPackage);
     expression.register_symbol_table(symbols);
 
     /* parser from exprtk */