Update gocupi.go

Add newlines after help text
added mercurial
added some stuff

serial comm.
path variables
Fill writeData buffer with 0s when about to pauseAfterWrite
Merge branch 'jromero-master'
Merge pull request changes with latest
Using a relative import path seems to break the ability to do go get, the absolute path works when running 'go build' from gocupi directory when you have your gopath set, it produces the gocupi.exe into the current directory
Fixes #3, changed to the typical go approach of returning an error code instead of using panic, which was a bad idea to do when validating user input
Fixes #2, you still have to put 3 numbers, but you can use 0 as a placeholder to skip updating a particular value, so you can do setup 800 0 0 and it will only change the horizontal distance, or setup 0 0 100 to only update right string length
Fix goroot setting in readme
Streamline quickstart