add cli, add method QRCode.Write(), update readme

[shenwei356]

Hi @skip2 ,

I add a command-line tool qrcode, which will be built into $GOPATH/bin/ when installing this package by go get. The command can generate QR code and immediately display using imagemagick command "display":

qrcode hello word | display

A method Write method is added for type QRCode so we can write to more output stream:

 func (q *QRCode) Write(size int, out io.Writer) error {}

README.md is also reedited mostly in Markdown format and updated for the CLI.

[shenwei356]

From the travis-ci log, it should not be the issue of code.

[skip2]

Try removing the "release" build from the .travis.yml. I think that line's just wrong, there's no go tag called "release", similar to here:

travis-ci/travis-ci#3076

[shenwei356]

Yes, it passed

[skip2]

This looks good, thanks! :)