Generated from git, so there may be duplicate authors
if someone used multiple mail addresses.

The big notice at the top of the release note is not interesting
 to most users now and apparently comes across poorly to some.

Better to provide more information about what we do support.

This disentangles the script validation skipping from checkpoints.

A new option is introduced "assumevalid" which specifies a block whos
 ancestors we assume all have valid scriptsigs and so we do not check
 them when they are also burried under the best header by two weeks
 worth of work.

Unlike checkpoints this has no influence on consensus unless you set
 it to a block with an invalid history.  Because of this it can be
 easily be updated without risk of influencing the network consensus.

This results in a massive IBD speedup.

This approach was independently recommended by Peter Todd and Luke-Jr
 since POW based signature skipping (see PR#9180) does not have the
 verifiable properties of a specific hash and may create bad incentives.

The downside is that, like checkpoints, the defaults bitrot and older
 releases will sync slower.  On the plus side users can provide their
 own value here, and if they set it to something crazy all that will
 happen is more time will be spend validating signatures.

Checkblocks and checklevel are also moved to the hidden debug options:
 Especially now that checkblocks has a low default there is little need
 to change these settings, and users frequently misunderstand them as
 influencing security or IBD speed.  By hiding them we offset the
 space added by this new option.

Just a quick run through some docs and fixing some text errors.

Now that 0.13 has branched, release notes for 0.13 should be maintained
there, and the release notes file on master is for 0.14 release
notes.

Closes #7681.

[skip ci]

The actual release process quite diverged from what was written here,
also clarify things a bit.