Positional bool parameters to control the rendering of the plot
have been a pain. We are down to one parameter (instant),
but more will be readded, so let's use the opportunity to
control rendering with a flags parameter.
Sadly, C++ has no reasonable way of defining flags that I know
of. Either the identifiers leak (enum), or can't be trivially
ORed (enum class) or are weakly typed (int). Let's just use an
integer for now.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
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