Added the (properly formatted) license file back,
the installer adds go\bin to the system PATH now,
the output package names are in line with the linux
and darwin versions, dist.bat extracts GOARCH in a
sane way, readme cleanup.

Tested on Windows 7 only. It would be helpful if
someone else could give it a try. See the readme
for details.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5673099