Improve support for component invocation

Improve invocation of component functions and add tests to ensure sub-components can be passed through attributes.

v0.1.1

This is most definitely a pre-alpha package. Use it at your own risk!

In this release, I've also cleaned up how we build on top of MarkupSafe and how we handle interpolation values with an __html__() dunder. This allows for clean interoperability with the Django and Jinja2 worlds; for instance, you could define a component function that returns a rendered Django or Jinja2 template, and the html() processor would correctly treat that as "safe" content to render as-is.

In addition to the :safe format specifier, we now also support an explicit :unsafe format specifier; see the README.

Initial release

This is the first pre-release version of html-tstring. It's usable, but there is much still to do.