pre_build hook now warns and skips the ribbit build if node or npm
are not installed, instead of failing the entire slam build.
Also, copy all of dist/ instead of individual files
This commit moves all html/markdown editor logic to the ribbit library.
Submodule tracks https://git.evilchi.li/evilchili/ribbit.git.
The dist files in static/ are committed copies; the submodule
provides source access for development.
We use pre_format and pre_build slam hooks to ensure the submodules are
initialized and updated correctly, and to perform the dist file copy.