Implement additional exercises

[BNAndras]

CLAIMED

• [ ] flatten-array - BNAndras
• [ ] queen-attack - dreig

COMPLETED

• [x] bank-account
• [x] binary-search
• [x] clock
• [x] diamond
• [x] food-chain
• [x] high-scores
• [x] kindergarten-garden
• [x] knapsack
• [x] luhn
• [x] minesweeper
• [x] pangram
• [x] parallel-letter-frequency
• [x] pascals-triangle
• [x] pig-latin
• [x] protein-translation
• [x] proverb
• [x] robot-simulator
• [x] run-length-encoding
• [x] secret-handshake
• [x] sieve
• [x] spiral-matrix
• [x] square-root
• [x] strain
• [x] two-bucket
• [x] yacht
• [x] zebra-puzzle

Don't auto-close the issue please.