added new method sequence_with_ambiguity that, for a given region, returns the Slice with ambiguity codes in the sequence
added new method sequence_with_ambiguity that, for a given region, returns the Slice with ambiguity codes in the sequence

dbolser-ebi/ensembl-variation,dbolser-ebi/ensembl-variation,willmclaren/ensembl-variation,Ensembl/ensembl-variation,willmclaren/ensembl-variation,Ensembl/ensembl-variation,dbolser/ensembl-variation,willmclaren/ensembl-variation,dbolser/ensembl-variation,dbolser/ensembl-variation,willmclaren/ensembl-variation,dbolser-ebi/ensembl-variation,dbolser/ensembl-variation,Ensembl/ensembl-variation,Ensembl/ensembl-variation,Ensembl/ensembl-variation,willmclaren/ensembl-variation