Adding about command line switch

Adding about command line switch and fixing exit code for help switch.  Fixes #52.

```bash
$ ngs-downsample-fastq -a
ngs-tools 1.5-SNAPSHOT
Commit: 0ef2155c72da2fcf854f6a49c0ff1e7212db9ba1  Build: 2014-11-05
Copyright (c) 2014 National Marrow Donor Program (NMDP)
Licensed GNU Lesser General Public License (LGPL), version 3 or later

$ ngs-downsample-fastq -h
usage:
ngs-downsample-fastq -p 0.5 [args]

arguments:
   -a, --about  display about message [optional]
   -h, --help  display help message [optional]
   -i, --input-fastq-file [class java.io.File]  input FASTQ file, default stdin [optional]
   -o, --output-fastq-file [class java.io.File]  output FASTQ file, default stdout [optional]
   -p, --probability [class java.lang.Double]  probability a FASTQ record will be removed, [0.0-1.0] [required]
   -z, --seed [class java.lang.Integer]  random number seed, default relates to current time [optional]
```