Crate depends on unix methods - does not compile on windows

This crate seems to only support unix, and relies on several unix-only methods from the stdlib, such as std::os::unix::ffi::{OsStrExt, DirBuilderExt, MetadataExt, OpenOptionsExt} and many more within localfs.rs.

Furthermore it seems to be relying on the runtime provided "case insensitive" flag to switch between windows and unix parts of the library, which is both unintuitive, and easily replacable with conditional compilation.

The correct behaviour should be to use the platform-independent methods as much as possible (for example replacing unix modes to open files with a rust file builder), then when necessary conditionally compile either unix or windows methods based on the compile target, or explicitly and clearly state that windows is not supported.

I have attached an example of the errors created when simply compiling the hyper example from the repo
output.txt

Seems like this PR should fix the problem? #7