Feature/incorporate optimist commandline options

I've gone ahead and done the work to incorporate the optimist js library in to avrodoc to support the following command line input options:

avrodoc input1.avsc input2.avsc --output=/tmp/newFile.html
avrodoc input1.avsc input2.avsc -o=/tmp/newFile.html
avrodoc input1.avsc input2.avsc --output /tmp/newFile.html
avrodoc input1.avsc input2.avsc -o /tmp/newFile.html
avrodoc -o /tmp/newFile.html -- input1.avsc input2.avsc
avrodoc --output /tmp/newFile.html -- input1.avsc input2.avsc
avrodoc --output /tmp/newFile.html -- -input1-with-hyphen.avsc

Please let me know when you've incorporated these changes as well as updated the npm website so we can pull a fresh copy down from there.

Thank you!

Micah