def completions_at filename, line, column
      position = Position.new(line, column)
      cursor = Source::Cursor.new(checkout(filename), position)
      api_map.clip(cursor).complete
    end
def completions_at filename, line, column
      position = Position.new(line, column)
      cursor = Source::Cursor.new(checkout(filename), position)
      api_map.clip(cursor).complete
    end
Get completion suggestions at the specified file and location.

 @param filename [String] The file to analyze
 @param line [Integer] The zero-based line number
 @param column [Integer] The zero-based column number
 @return [SourceMap::Completion]
 @todo Take a Location instead of filename/line/column