Building standalone binaries on linux working.

Mostly changes to cook and jpm. Also some
code for file associations in the windows installer, and
adding the :linux value from os/which (instead of just :posix).

src/core/corelib.c

@@ -270,6 +270,7 @@ static Janet janet_core_native(int32_t argc, Janet *argv) {
         janet_panicf("could not load native %S: %S", path, error);
     }
     init(env);
+    janet_table_put(env, janet_ckeywordv("native"), argv[0]);
     return janet_wrap_table(env);
 }