Update DEVELOPERS.md

[kcArtemis]

I have tried to complete the programming_problems (EXAM.md)

[iankorf]

• Generally inconsistent use of capitalization and spacing.
• Factorial enters an endless loop with -1 input
• Statistics: You have embedded functions inside conditional statements (weird from my perspective). You calculated mode, which wasn't requested. Makes me think you looked it up.
• Birthday: The problem didn't say you were supposed to use sets, but it's okay and clever.
• Hydropathy: Dictionary initialization is ugly. Again with the embedded functions.
• AA: OK
• IPC: Hard-coded output file name is bad. Code is massively indented.
• FASTA: This isn't a library. This isn't the case for a data frame.
• Entropy: Did not use library as requested. Not really a place for data frames. That's not how you make a program executable.
• Overlaps: Duplicate code instead of function for reading GFF. Doesn't get the right answer. Not sure about efficiency.