Write a program in Ruby that parses a dictionary file for unique sequences of letters.
Requirements:
- The program should generate two output files, "sequences" and "words".
- The sequences file should contain every unique sequence of four letters that are unique and appear in exactly one word of the dictionary file.
- Differences in casing should not reflect a unique sequence.
- Numbers and special characters should not create a unique sequence.
- The words file should contain the corresponding words that contain the sequence, in the same order, again one per line.