An unquoted empty value followed by an inline comment (e.g. `KEY= # comment`)
was parsed as the comment text because the equal-sign regex consumed the
whitespace after `=`, leaving no whitespace for the comment-stripping rule to
match. When the value is empty (whitespace follows `=`) and starts with `#`,
treat the rest of the line as a comment and the value as empty. Values with no
space before `#` (e.g. `KEY=#novalue`, `KEY=a#b`) are unchanged.

Closes #600

Credit @Noethix55555 for fixing inline comment on empty unquoted values.

Fixes #697.

Fixes #708

Fixes #699