The module searchers in the `require` package should return a string
if the module is not found, and not raise an error.
See: https://www.lua.org/manual/5.3/manual.html#pdf-package.searchers
Also make error strings contain newlines and tabs just like the original
ones.
- Remove file related functions from loader.
* All packages must be builtin.
- Remove os.tmpname.
- Interface with TLSF.
- Don't abort() when out of memory.