Renamed `Container.contents` to `Container.content` to be in line with
the corresponding `Element` function name. This has also been done for
the properties structs used by the `Container`.
This could also be done through the `resize` function interface of the
`Element` or the corresponding `Container` from the outside (as done in
this example - as the size is know at compile-time).
This also means that currently the dynamic resizing through the app's
detached thread is not working, as it cannot send size updates. The
examples have been overhauled to still implement intermediate mode
applications accordingly.
Improve some examples to provide visual feedback, i.e. for the button
exmample, with fixes to make them compilable with the `Scrollable`
element changes.
This also contains some minor refactoring to improve the readability
and understandability of the library (i.e. renaming of Style.Attributes
to Style.Emphasis).
