Subclass errors from a general Lotus module error

[liamdawson]

Closes #81

[jodosha]

@liamdawson Hello, and thanks for this contribution. Can you please name it Error, instead of ViewError? Thanks! 👍

[pascalbetz]

No need to add that constructor

[liamdawson]

@jodosha and @pascalbetz — made your suggested adjustments.

[pascalbetz]

Just a thought: is there something like a search path in lotus or what extensions were searched? Then this would be useful information in the exception message.

[jodosha]

@liamdawson Thank you, merging this. 👍

[jodosha]

@liamdawson I've cleaned your PR with 847b7da, because MissingTemplateError and MissingFormatError were still inheriting from ::StandardError.

I also moved all the errors in one file (lib/lotus/view/errors.rb) in order to don't require lotus/view/error everywhere, and because I wanted to put all the errors on the same namespace depth. For instance, the commit changes Lotus::View::Rendering::MissingTemplateLayoutError into Lotus::View::MissingTemplateLayoutError.

Can you please follow the same approach for the other frameworks? Thank you very much. ✨