:theme option should be an Elixir module rather than a simple atom

[andreapavoni]

Hi there,

as stated in the title, it would be very useful to provide an elixir module name rather than a simple atom as :theme option in Kerosene.Html module.

This change would let devs to implement custom themes for their projects more straightforwardly.

[allyraza]

Hi @andreapavoni, we could add this feature indeed this will be very useful let me look into it