Change `master` to a more positive name

[jonrkarr]

Posting this here because I'm not aware of a more appropriate place. Feel free to transfer this elsewhere.

The issue

Because master has negative connotations, many people are replacing the term master with other terms such as main. Here's an article about GitHub's change from master to main.
https://www.theserverside.com/feature/Why-GitHub-renamed-its-master-branch-to-main

In addition, I think the meaning of the master could be clearer. For example, is this intended to indicate the SED-ML files that should be executed? Should files that have master=false not be executed? What should happen if no file has master=true? What is the only file that has master=true is not a SED-ML file (e.g., the only master file is a .cps file)?

Proposal

• Rename the master attribute to something like main.
• Clarify in the specifications how a positive value of this attribute should be interpreted.

[matthiaskoenig]

Personally, I think there are more direct actions we can take to demonstrate that we are inclusive and politically correct. The main problem I see with the renaming is that it adds additional work in terms of

• update attributes
• update libraries
• incompatibility of archives
• breaking software
  and so on.

I would prefer more direct measures such as

• adding a code of conduct to the COMBINE libraries
• adding clear statements on inclusiveness, ... and so on
  which will not add additional work on the developers and users of COMBINE archives.

[jonrkarr]

These should also be done, but they don't address the issue with the syntax itself.

libCOMBINE can maintain aliases to getMaster, setMaster, etc. to avoid developers needing to make changes.