Add example of writing fastq

[kyleabeauchamp]

#471 asked for fastq writing capabilities. I think we already have this, but it's a bit hard to find. Basically, the __str__() member function FastqProxy does what we need for writing, so we might as well add an example of this.

for line in fastq:
   fh.write(str(line))

The only other thing that might be desirable is to have a constructor for FastqProxy that creates an object from the name, seq, and qual strings.

[AndreasHeger]

Good points, I will see if I can polish this part this weekend.

[AndreasHeger]

Done, see 1c28fcb