Tell templates where they're being rendered

[arctic-hen7]

Is your feature request related to a problem? Please describe.
Right now, web_sys panics if you call it on the server, and detecting if you're on the server with it is difficult and badly documented. Thus, it's very difficult to have client-side-only logic in Perseus, which is really a must for any framework like this.

Describe the solution you'd like
Perseus should provide a simple boolean argument to templates along with their state telling them if they're being rendered on the client or the server. This will make things orders of magnitude easier!

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[arctic-hen7]

This will be released in v0.2.3.

[arctic-hen7]

Also, this doesn't use a boolean parameter, but a context element, and provides a macro is_client! for checking easily in a reactive scope.

[arctic-hen7]

Alright, my two solutions for this thus far have broken other parts of Perseus, so this is going to be a little harder than I thought!

[arctic-hen7]

Okay, this will be released in v0.3.0 along with a refactoring of all errors to use thiserror instead of error_chain. If anyone figures out how to do this in just web_sys, please tell me! For now, it's done by explicitly passing in a boolean from the renderer (server says it's rendering on the server, client says it's hydrating on the client).