encode pattern for composing variables

[haraldschilly]

downstream sagemathinc/cocalc#3156

To make this language and template independent, this could be a list of strings and integers. Integer 0 is the "key" (variable name) and 1 is the value. The setup variables are a map of <key, value>. The strings are the fill-in for the respective programming language. Any processing then concatenates the strings without a space sign (thinking of bash!). e.g. [0, " = ", 1] for the "usual" case, [0, " := ", 1, ";"] for gap, ["setVar(", 0, ", ", 1, ");"] for a more unusual pattern.