Updated examples get_profile and create_posts in line with new API

[clockworkpc]

The current examples use the /me endpoint and try to identify the profile by the following URN string:
f"urn:li:person:{me_response.entity['id']}.

However, I found that even though I have a valid 3-legged-token with the necessary scopes enabled, I was getting an error.

I believe that the most recent changes to the LinkedIn API require the following changes:

1. /userinfo GET endpoint instead of /me
2. me_response.entity['sub'] instead of me_response.entity['id']

There are some further differences in the names of the fields returned by the userinfo and me endpoints, which are reflected in the proposed changes in the example get_profile.py.

[clockworkpc]

I also wrote a tidier script that focuses on the new API:
https://gist.github.com/clockworkpc/c311d4aea82d8b5adc27bbb6382455ee