Add extension method for specifying horizontal and vertical padding.
Similar constructor for `Padding` already existed.
Update documentation for table column appearance (padding).
Update
`Should_Render_Padded_Object_Correctly_When_Nested_Within_Other_Object`
test to use new extension method.
Removed the verbs from all extension methods that manipulate
properties which makes the API more succinct and easier to read.
Also added implicit conversion from string to Style.
As a good OSS citizen, I've obsoleted the old methods with
a warning for now, so this shouldn't break anyone using
the old methods.
