Defines the basic attributes of a markup renderer.

A renderer needs to implement a compile/2 function and an optional ast/0 function. When a markup file is being compiled, a module is created on demand. This module imports all template helpers defined by Still as well as any template helper configured by the user:

config :still,
  template_helpers: [Your.Module]

The created module implements a render/0 which will return the result of the compile/1 call.

The ast/0 can be used to tap into the AST of the new module and import or require any necessary module.

Markup renderers should use Still.Preprocessor.Renderer and provide two options:

• :extensions - the list of extensions compiled by the renderer;
• :preprocessor - the preprocessor used to render any necessary snippets (e.g via Still.Compiler.TemplateHelpers.ContentTag).