Revise BSIP-01: BSIP Purpose and Guidelines

The [[BSIP-01: BSIP Purpose and Guidelines](https://github.com/bitshares/bsips/blob/master/bsip-0001.md)] document is a bit outdated, and also contains wording that can be improved.

* BSIP Editors. There are 3 editors listed in BSIP-01. However, among the list, only @xeroc is still relatively active in the community, in the meanwhile other community members have been taking time doing the editors' job. How to choose editors probably worth discussing.

* The process. E.G. we're heavily relying on Github to collaborate, but not sending emails back and forth.

* Shareholders. It's mentioned by some community members that we should avoid using the "share" word due to concerns about laws.

* The description about "accepted" status is confusing.
> People wishing to submit BSIPs first should propose their idea as github issue first. After discussion you will be assigned a number for the bsip and can send a pull request for your draft. Once consensus among discussion participants is reached, the status can be switched to *accepted*. From this time on, major changes of the document will not be permitted.
> ...
> Once a BSIP has been published, the reference implementation must be completed. When the reference implementation is complete and accepted by the shareholders via approval voting, the status will be changed to **"Accepted"**. A BSIP can also be "Rejected" by shareholders.

Maybe there are more elements that can be updated.