Added changes that fixed issues with my implementation

Hello Michael

1. README.md states that for installation, you have to run pip install linkedin -- however if someone wishes to add scope to the request, in version 0.1.2, permissions is not part of LinkedinAPI::__init__() property list. To fix this, I added a minor text change in the README.md file. The user should now call, pip install linkedin==0.1.3. I noted that when I called pip install linkedin after someone else had bumped the version 0.1.3, pip was still installing version 0.1.2.

2. When trying to retrieve a requestToken and then accessToken, we were doing this by 'GET' method. However, documentation in http://developer.linkedin.com/documents/authentication states that these calls need to be of type 'POST'.  -- I think there is a previous Pull Request with this change by evandekieft 

3. While revising how to implement authentication with Linkedin, I noticed that the documentation on http://developer.linkedin.com/documents/authentication stated that the authorize url is: https//www.linkedin.com/uas/oauth/authenticate?oauth_token=XXXXXXXXX. I also notice a very  strange behavior when using the aus/oauth/authorize link, it kept asking me to "Allow access" even though I had given access rights to the application. After switching to the url specified in documentation, I was requested to "Allow access" once, and thereafter, it would just redirect me to the correct authenticated callback url stated in the application callback url field.


Thanks,
-e