F# writer/visitor

[zspitz]

There might be value in having a writer/visitor that produces F# syntax for expression trees.

Additionally, it might be useful to have a writer/visitor that generates the code needed to produce code quotations via the factory methods at https://fsharp.github.io/fsharp-core-docs/reference/fsharp-quotations-fsharpexpr.html.

Will also require F# support in utility functions: https://github.com/zspitz/ZSpitz.Util/issues/14