Support stdin/stdout in sam.reader and sam.writer

[msto]

It would be helpful if sam.reader() and sam.writer() supported the special cases of "-" and/or "stdin" and "stdout" to open sys.stdin and sys.stdout directly for reading/writing

to avoid verbosity like the following

in_bam_path: SamPath = sys.stdin if str(in_bam) in ["-", "stdin"] else in_bam

out_bam_path: SamPath
out_file_type: Optional[SamFileType]
if str(out_bam) in ["-", "stdout"]:
    out_bam_path = sys.stdout
    out_file_type = SamFileType.SAM
else:
    out_bam_path = out_bam
    out_file_type = None
    
with (
    reader(in_bam_path) as bam_reader,
    writer(
        out_bam_path,
        header=bam_reader.header,
        file_type=out_file_type,
    ) as bam_writer,

[nh13]

Implemented in #69