This is a starting point to dynamically loading `markdown` files as blog
entries. With this change the *doc/about.md* and *doc/blog.md* files
are no longer builded into the executable and instead read from the
filesystem during runtime (along with the new test file *doc/test.md*).
With functional increments in `zterm`'s `Scrollable` `Element`, an
implementation (such as `Content`) can provide a size hint for the
minimal required size to dynamically change its dimensions for the
scrollable `Container` in the `Scrollable` `Element`.
