I was surprised to see so many legacy lambda syntax examples in the
documentation. This replaces all of them with the new syntax -- excluding
the handful of cases meant to explicitly verify the legacy form is still
valid. This also adds a link to the issue in the release notes which
documents the change in syntax.
Related #664
I noticed that most places in the documentation that emit a "note"
about Elvish behavior use `**Note**:`. There were two places that use
all uppercase. Make those consistent with the other uses. Also clarify
the note associated with the `not` builtin.
Document that an unqouted `#` character has special meaning to the Elvish
parser in the context of passing `#RGB` values to the `styled` command.
Also document the `fg-` color name prefix.
