Feature Request: create a EVID translation function

[mattfidler]

Something like:

rxode2({
    # This changes evid=1 to evid7
    evid1to(depot, 7)
    # This would indicate that instead of a typical oral dose
    # This is a transit compartment dose
    k           <- cl/vc
    ktr         <- (n+1)/mtt
    d/dt(depot) <- transit(n,mtt,bio)-ka*depot
    d/dt(cen)   <- ka*depot-k*cen
})

Then the translation occurs on etTrans() when it translates to the
classic evid it will not translate again.