Command-line -t requires from wrong directory

[hildjj]

In a directory other than <PEGGY_ROOT>/bin, this fails:

touch ast.js
echo '{{ require("./ast.js") }}\nfoo="1"' | peggy -t 1

the eval at the heart of the test routine is relative to the CLI script. I think there's a similar issue when we have {output: "parser"} in the API.

Some combination of vm and require("module").createRequire (when it's available) might be needed. Probably also making __dirname and __filename match the outputFile if it's not "-", and using cwd and a synthetic name when it is "-".

In node 10, createRequire doesn't exist, but the undocumented createRequireFromPath does, as well as new Module(path).require.

I don't know how to fix this for import, but we can probably at least hack in import.meta.url same as __filename.