added failing tests
improved functionality of repr

Before:
======================================================================
FAIL: complement functions as expected
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tests/test_core/test_sequence.py", line 183, in test_complement
    self.assertEqual(self.b1.complement(),DNASequence("CTAATGT"))
AssertionError: CTAATGT != CTAATGT

After:
======================================================================
FAIL: complement functions as expected
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tests/test_core/test_sequence.py", line 183, in test_complement
    self.assertEqual(self.b1.complement(),DNASequence("CTAATGT"))
AssertionError: <NucleotideSequence: CTAATGT (length: 7)> != <DNASequence:
CTAATGT (length: 7)>
fixed failing test of repr
fixed failing tests, added equality operators
defined ne more explicitly
added tests
added equality and inequality tests