Add more how-to guides

[ddinu]

Add how-to guides for subjects and values.

[jcmana]

Hello, I was browsing through the "Getting started" and "Articles" on documentation page and I couldn't find any example showing multithreading environment. Is this supported by the library? Thank you

[ddinu]

Multithreading is supported in the sense that you can subscribe to events concurrently and trigger them concurrently. When events execute callbacks and update values, they will run on whatever thread triggered the event. So, you just have to make sure that your callbacks are thread safe, and the rest should work.