An implementation of interpreted string literals, inspired by Python's Literal String Interpolation <https://www.python.org/dev/peps/pep-0498/> and Docstrings <https://www.python.org/dev/peps/pep-0257/> and Julia's Triple-Quoted String Literals <https://docs.julialang.org/en/stable/manual/strings/#triple-quoted-string-literals>.
copied from cf-post-staging / r-glue