Add --prefix option to tests/parse.js to more easily test i18n.

This now works:
echo '[[Archivo:Nombre|thumb|alttext]]' | node tests/parse.js  --prefix=es

gwicke: Also rename wgScript to apiURL and remove the unused wgScriptPath and
fetchConfig options.

Change-Id: I265d4cd38d9ce5964cf9be4ba59068516c016cf6
Merge "Add --prefix option to tests/parse.js to more easily test i18n."