Update codemeta conversion to codemeta v3.0

CLARIAH Tool Discovery now outputs codemeta v3 instead of v2. 
The changes between v2 and v3 are not big, but please do take note of                                                            
what changed. Here are my release notes for codemetapy 3.0.0:

* https://github.com/proycon/codemetapy/releases/tag/v3.0.0

And from codemeta itself:

* https://github.com/codemeta/codemeta/releases/tag/3.0