At least in neovim, `│vi:` is not recognized as a modeline because it
has no preceding whitespace. After fixing this, opening a file yields
an error because `net` is not an option. (`noet`, however, is.)
This change improves the way internal APIs are being hidden behind the
`COSMO` define. The cosmo.h header will take care of defining that, so
that a separate define statement isn't needed. This change also does a
lot more to define which APIs are standard, and which belong to Cosmo.
This change brings page faults for precompressed static asset serving
down from 27 to 20 (or fewer) after fork. This is more of an art than
science. Hopefully Blinkenlights can visualize page faults soon.
