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
3 files changed