Library depends on same-file

[FreeMasen]

Currently even the library associated with this project will require that it is compiled on either unix-like or windows target because of a transitive dependency. same-file is a dependency of walkdir which has 2 architecture dependent implementations of it's functionality. While the direct dependency on walkdir is in the dev-dependencies section, which would avoid any issues for users of the mdbook library, it happens to be a dependency of handlebars as well. The handlebars crate has a feature gate to remove this depenency (no_dir_source) which would remove this problem.

According to the unit tests adopting this feature shouldn't break anything.

[Dylan-DPC-zz]

Fixed by PR linked (#903). Thanks