Add ability to open remote files

This could either be accomplished by modifying `loam.open()` to detect URLs, or by creating a new method specifically for the purpose of opening remote files.

Either way, the corresponding Emscripten file will need to be created using [`FS.createLazyFile()`](https://kripken.github.io/emscripten-site/docs/api_reference/Filesystem-API.html#FS.createLazyFile).

Start at loam.open() and review how the Emscripten file is created. Check the FS.createLazyFile() documentation and determine whether remote URLs belong in loam.open() or a new method. Done means a remote file can be opened and its corresponding Emscripten file is created.

Written by the indexing model from the issue text.