Fix ReadPair's never being freed

[Donwulff]

Fixes memory leak in PairEndProcessor::interleavedReaderTask() where ReadPair objects were not being freed, resulting in a leak of 16 bytes per read pair across the input (Issue #392 ).

Changes:

• Modified call signatures to reuse the same ReadPair for all reads, as it's a return container for the Read pairs.
• Added a method to detect the end of input for clarity.
• Updated freeing of the Read arrays to utilize array delete.

Performance Metrics Comparison on 1KG HG00312 exome with 110M reads:

Metric	Before	After
User time (seconds)	1524.60	1507.94
Maximum resident set size (kbytes)	4423400	2548668

All results remained identical.