Fix some overload tags in YARD docs

This patch indents `@param` tags that are associated with an `@overload` tag like suggested here (and already applied in other parts of the code): http://rubydoc.info/gems/yard/file/docs/Tags.md#overload

It further fixes some instances where the YARD docs are broken: http://rubydoc.info/gems/sass/3.3.2/Sass/Script/Functions#change_color-instance_method
(look below "examples" where the overload signature continues unintentionally)