Enable concatenation of flows

[mgeipel]

@NAME is used as a place holder. This allows for joining of several flows. The pattern can be used to implement an equivalent of an SQL join.

"A"|
template("${o}")|
template("x${o}")|
@X;

"B"|
template("x${o}")|
@X;

@X|
template("${o}")|
write("stdout");