feat(windows compatibility): correct paths where necessary

A few changes:
- where cli and amd_compiler use functions of path to create filenames for
 inclusion in AMD define/require calls, replace backslashes with
 forward slashes as is necessary for require/define syntax
- FakeFileSystem internally represents paths given to the constructor in
 native format (this means backslashes in windows).
- FakeFileSystem normalizes parameters that represent paths so that they
 conform to the native path format for the platform.
Merge pull request #16 from stu-salsbury/windowsCompatibility

feat(windows compatibility): correct paths where necessary