Consolidate file-system-loader

[joshwnj]

#64 introduced a babelified copy of file-system-loader.js from css-modules-loader-core as a stopgap while a solution was being worked out.

Once other related issues are resolved we'll need to either PR the new file-system-loader back into core, or at least make our own version which is more pleasant to read.

[tjallingt]

@joshwnj what is the status on this? As I understand it the PR into the core has been made but not approved (as a matter of fact nobody seems to have worked on the loader-core for 2 months).
To me, using windows to develop, this is an issue preventing me from using css-modulesify in my projects...

[joshwnj]

@tjallingt thanks for your patience on this - I've been away over the holidays but hoping to make some time early this week to review & get this sorted out.

[tjallingt]

Great, thanks for your response.
Hope you enjoyed your holidays 😄