Change paths from YAML to unix paths before parsing.
Change paths from YAML to unix paths before parsing.

This allows all OSes to understand the path. os.path.normpath will take
care of changing it back to using backslashes if running on Windows.

Fixes #397.

sarahmarshy/project_generator,project-generator/project_generator,ohagendorf/project_generator,0xc0170/project_generator