Windows friendly

The first thing I noticed upon loading the Windows portable package was that I could not actually read README.txt (using notepad, which is the default application for reading .txt files on Windows). 

  Next, I tested a kivy demo and discovered that the "python" command on my workstation had been hijacked, so that I was running the older Python from kivy (2.7.3) rather than the current version which is installed on my workstation.  Then, I could not fix that by editing the kivy.bat file using notepad, again because of unix line endings.

  This patch fixes those problems, also adding a short blurb suggesting the Python Launcher for Windows as an option for starting kivy programs. 

  Kivy.bat now changes the Windows prompt subtly (changing ">" into "=") while the kivy-modified cmd shell is running.

I use PyCharm, so I also entered the PyCharm project memory to the entries in .gitignore, as a tiny side effect.

Caution:  I could not find the instructions for creating a new portable package, so was not able to test a new distribution -- I could only test the changes themselves.  The added .gitattributes file preserves the Windows line endings correctly on my Ubuntu development system.