Added new methods:

    $exon->cdna_start($transcript);
        # Returns the start position of the exon in cDNA coordinates.

    $exon->cdna_end($transcript);
        # Returns the end position of the exon in cDNA coordinates.


    $exon->cdna_coding_start($transcript);
        # Returns the start position of the coding region of the exon
        # in cDNA coordinates.  Returns undef if the whole exon is
        # non-coding.

    $exon->cdna_coding_end($transcript);
        # Returns the end position of the coding region of the exon
        # in cDNA coordinates.  Returns undef if the whole exon is
        # non-coding.


    $exon->coding_region_start($transcript);
        # Returns the start position of the coding region of the exon in
        # genomic coordinates on the forward strand.  Returns undef if
        # the whole exon is non-coding.

    $exon->coding_region_end($transcript);
        # Returns the end position of the coding region of the exon in
        # genomic coordinates on the forward strand.  Returns undef if
        # the whole exon is non-coding.


Since an exon may be part of one or more transcripts, the relevant
transcript must be given as argument ot these methods.