Quick Fix for #153

In the spirit of fixing, rather than whinging, this is a quick fix for my issue #153.  Splitting paths on `:` in `drake.fs$split-path` returns `('C', '\\data\\test.csv')` for properly formed windows paths.  This causes `drake.fs$get-fs` to return `[fs, 'C', '\\data\\test.csv]`.  So, a basic function e.g. `(fs di/data-in? "C:\\data\\test.csv")` goes to `(di/data-in? fs '\\data\\test.csv')` which clearly breaks for windows.  

Splitting on "://" should still get the correct prefixes for e.g. s3://bucket.blah or hdfs://... without mangling the windows paths.  

Note: It seems like there may be a different (and possibly cleaner?) solution to this using make-path more liberally, but it wasn't clear to me exactly where to use that, and this worked.  Hence, the quick-fix appellation.