Implement external memory algorithms

Create implementations for external memory (disk-based) algorithms:

## Fundamental techniques:
- Blocked access patterns
- Multi-way merging
- Buffer trees
- Streaming algorithms
- Disk-based data structures

## External memory algorithms:
- External merge sort
- External B-trees
- Disk-based hash tables
- External memory graph algorithms
- Buffered repositories

## Applications:
- Big data processing
- Database systems
- Large file manipulation
- Geographic information systems

## Requirements:
- Provide I/O complexity analysis
- Include memory hierarchy considerations
- Create realistic testing scenarios
- Document practical applications and limitations

This collection will demonstrate algorithm design techniques for scenarios where data doesn't fit into main memory, which is critical for big data processing and database systems.