Remove unused fmt pkg import
Rename package to nexmo

Having 'go' in the name is not needed, dropping it in favor of just
using 'nexmo' makes the usage clearer and more concise.
Use enviroment variables to store testing credentials

Instead of forcing users to edit the file and include their API
credentials, where they could potentially end up checked in to their git
repository and/or end up posted on Github, use enviroment variables to
store them.

They can be set globally by exporting them, then calling the program, or
you can pass them to `go test`:

NEXMO_KEY=something NEXMO_SECRET=something NEXMO_NUM=18005555555 go test
Update README.md

Add a godoc button, update examples
Wrap lines at 80 characters

Improves readability, especially in terminal editors and on Github.
Remove erroneous comment
Cleanup sendMessage()

Convert is_flash_message to camel case
Simplify declaration of all the string arguments
Merge pull request #3 from inhies/f.cleanup

F.cleanup