added calculation of percent GC and printing result to stdout

[gtiley]

Description

Calculated percent GC by counting characters in sequence strings from a fastq. Uses only bash on lines 30-41 of fastq-peek.sh

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Tested by recovering correct percentage of 50% from sample.fq test data included in repo. Assumes only ACGTN nucleotides are present in fastq files.

Checklist:

• My code adheres to the repository style guide
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing tests pass locally with my changes