`:` in region strings passed to `--chrom`
Region strings passed to `--chrom` can be of the format `ref_id:start-end` to only consider part of a reference sequence. However, reference sequences sometimes have `:` in their sequence name (e.g. if they were created with `samtools faidx`. In this case, `mosdepth` fails with `chromosome name ... not found` if the whole reference name is provided (see example below).

Example:
```
$ samtools view -h example.bam
@HD     VN:1.6  SO:unsorted     GO:query
@SQ     SN:seq:1-100    LN:100
@PG     ID:samtools     PN:samtools     VN:1.19 CL:samtools view -h example.bam
read    0       seq:1-100       1       4       100M    *       0       0       AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA *       NM:i:0  ms:i:200        AS:i:200        nn:i:0  tp:A:P  cm:i:85 s1:i:100        s2:i:98 de:f:0  rl:i:0

$ mosdepth test example.bam --chrom seq:1-100
[mosdepth] chromosome seq not found
```

In contrast, `samtools` commands work with sequence IDs that contain colons (see example below).
`samtools` example:
```
$ cat ref.fa
>seq:1-100
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

$ samtools faidx ref.fa seq:1-100
>seq:1-100
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

$ samtools faidx ref.fa seq:1-100:50-60
>seq:1-100:50-60
AAAAAAAAAAA
```

Could `mosdepth` be adapted to do the same?

Many thanks!