implement seqs2 feature as requested by James

[heartnetkung]

Add new feature

• allow nearest neighbor comparison to be done across 2 sets of sequences resulting in N2*N combinations
  • compared to before, when 1 set of sequences is given, every sequences are compared against every other sequences resulting in N**2 combinations.

Fix broken feature

• fix symspell algorithm not performing input validation
• incorrect output of sparse matrix

Example below

    test_input1 = ["CAAA", "CADA", "CAAA", "CDKD", "CAAK"]
    test_input2 = ["CDDD", "CAAK"]
    test_output = [(1,0,1), (1,2,1), (0,3,1), (1,4,0)]
    assert set_equal(symspell(test_input1, max_edits=1, seqs2=test_input2), test_output)

[heartnetkung]

@jhenderson0 It is done :)

[jhenderson0]

Great, thank you!