Case sensitivity on metadata directories

[pwrightcertinia]

Recently reported error due to an object having the folder structure of Object__c/Fields rather than fields. The metadata was not found.

We should be case insensitive on (all? or most) source directories. Investigate

[kjonescertinia]

Using uppercase in labels and fields did not appear to break anything in a test, but using "Objects" rather than "objects" did so its all a bit inconsistent. We could look to add a warning on wrong case use but I think it would be better for us to handle more generically as part of #97 where we can have stronger enforcement of metadata structure.

I will close this and note on the MDAPI issue.