Gff2mss

* Support for ambiguous "N"-base in fasta. ("N/n"-base will be converted to "assembly_gap" feature in MSS). Please install "gffpandas" library.

* According to the "N"-base supporting, "artificial_location" qualifier was adopted to mark the modified exon/CDS by GFF2MSS. To fix frameshift caused by "N"-base gapping, V.4.0 cut 1-2 bases of the exon as necessary. These artificially modified mRNA data will be marked with this qualifier on the MSS file.

* Processing speed was improved by using pandas (e.g., v3 = 14.8s, v4 = 4.2s).

--pid option is available to marge the previous protein ID to the new submission.
"[entry]", and "[submitter_seqid]" were used in submitter_seqid.

A script bug was fixed.

- rRNA and tRNA gene models were supported.
- A utility for tRNAscan result processing to gff3 file was applied.
- The license was changed from CC BY to the MIT License