Implement ret="all" in coords #47
Description
Followup of issue #40.
It might be useful to return every coordinate possible in coords. This could be done by adding a special ret value of "all" (verbatim).
Warning: this cannot be abbreviated, as this would change the current behavior of ret="a" which is to return accuracy. It cannot be mixed with any other value, and therefore only an exact match with a vector of length 1 should be allowed.