C++ tests are always run on `make cpp-tests` and `make cpp-test`
Extract stencil HTML methods to `stencil-html.cpp`
Extracts stencil I/O methods to `stencil-io.cpp`; other tidy-ups
Removes stencil embedding functions (for creating stencils using code)
Extracts serving related functions/methods to `stencil-serve.hpp`
Python package fixes
R package fixes
Various stencil fixes