- Added extra doctests
- Resolved issues:
- Issue #5: Running sequtil.property_ctd on sequence with length 1 results in float division by zero
- Issue #4: Autocorrelation functions result in error if len(seq) == lag
- Issue #3: Pseudo-amino-acid-composition calculation results in error if sequences contains ambiguous amino acids
- Issue #2: Incorrect pseudo amino acid composition type 1 and 2 if len(seq) < lambda
- Issue #1: Cannot calculate di-letter counts if seq contains letters that are not in alph.