Limit use of require("path") to resolve Windows compatibility issues

This pull request is to eliminate the use of `require("path")` in order to resolve issues with Windows.

First, the alias has been updated to not use path.join.  Using path.join changed the path names from using forward slashes to backslashes on Windows, but kept them as forward slashes on Linux.  Now, the alias will consistently use forward slashes.

Second, the file path has been updated to not resolve to an absolute path.  Use of absolute paths was exposing the local file system's absolute path in the client source in browserify (rendr, for instance, would expose the location of the `app/router` file in the client-side mergedAssets.js file).  While this can work, it is not ideal to expose the absolute path.  Now, the user can choose whether to use a relative or absolute path based on the `cwd` option.
For the alias, you always want forward slashes, as that is what developers are going to use.

For the filePath, we use forward slashes, unless it's an absolute path, then we will use path.resolve, which will return an OS-specific path.  In the case where cwd is an absolute Windows path, path.resolve will still get it right:

```
> path.resolve("c:\\test/fixtures/target")
'c:\\test\\fixtures\\target'
```