Support `|` as a macro

[Matvey Aksenov]

Some other libraries use the

{{ x | f | g | h }}

syntax to mean

{{ h(g(f(x))) }}

While anyone who knows what aesthetics means would prefer the latter form, we'd have to support the former variant due to the sheer volume of lesser templates written.

[Matvey Aksenov]

There are also abominations such as

{{ x | f(y) | g(z) }}

that mean

{{ g(f(x, y) z) }}

unfortunately.

[Matvey Aksenov]

I don't think we need to support abominations though, because our functions are not flipped in the first place.