Added `pathSeperator` option and slightly changed the plugin API to accommodate it. The API is backwards compatible; you can still pass the plugin an object `{ cwd, pattern, expose }` or an array of such objects. However, you can now pass an object such as `{ pathSeperator, entries }` where entries is an array of mappings. This matches the browserify terminology. If `pathSeperator` is not provided on the `options`, it uses `path.sep` (the system default). This commit also includes two additional tests for overriding the path seperator, and modifies the original test to use `path.join` so it will succeed on all systems.

Expanded docs to include example with path separator override and fixed spelling.