Adding ngs-generate-bed tool

```bash
$ ngs-generate-bed -h
usage:
ngs-generate-bed [args]

arguments:
   -a, --about  display about message [optional]
   -h, --help  display help message [optional]
   -o, --bed-file [class java.io.File]  output BED file, default stdout [optional]
   -n, --n [class java.lang.Integer]  number of BED records to generate, default 1000 [optional]
   -s, --size [class java.lang.Integer]  chromosome size, default 100000 [optional]
   -c, --chrom [class java.lang.String]  chromosome name, default 1 [optional]
   -l, --mean-length [class java.lang.Double]  mean length, default 100.0 [optional]
   -v, --length-variation [class java.lang.Double]  length variation, default 10.0 [optional]
```