The `# -*- coding: utf-8 -*-` headers were useful for Python 2, and
aren't needed for Python 3 where UTF-8 is the default.
yamllint support of Python 2 was dropped in early 2021, see commit
a3fc64d "End support for Python 2".
Let's drop these headers.
Instead of iterating over lines and tokens (and find comments between
tokens in the comment rules), add a new `Comment` type and set rules
with `type = 'comment'`.
Using either 'yes', 'no' or 'whatever', the user will be able to choose
whether to force block sequence items to be indented, to force them not
to be indented, or don't care, respectively.
Previously only comments that were indented like the following content
line were allowed, e.g.:
prev: line:
# commented line
current: line
With this change, such new cases are also allowed:
prev: line
# commented line 1
# commented line 2
current: line
