Amend CI script to new statuses and update existing status field values
in table and BIPs.
```
sed -z -i 's/Status: Proposed/Status: Complete/' bip-0*.md
sed -z -i 's/Status: Proposed/Status: Complete/' bip-0*.mediawiki
sed -i 's/| Proposed/| Complete/' README.mediawiki
```
- Update all Accepted status to Proposed (renamed status)
- The BIP Comments preamble headers added to every BIP
- The License preamble headers have been added to all BIPs with a Copyright section
This came up on the mailing list.
yyyy-mm-dd (ISO 8601) is the internationally accepted format for numeric
dates. This commit changes all BIPs to use that instead of dd-mm-yyyy.
It also updates BIP 0001 to prescribe the new format.