Map file types (extensions) to strategy types.

def get_file_type_map():
    """Map file types (extensions) to strategy types."""
    file_type_map = {}
    for strategy_type in get_strategy_types():
        for ext in strategy_type.file_types:
            if ext in file_type_map:
                raise KeyError(
                    'File type {ext} already registered to {file_type_map[ext]}'
                    .format(**locals()))
            file_type_map[ext] = strategy_type
    return file_type_map