[hooks] Memory hook feedback

[addyosmani]

Our React Hooks currently return a number of different kinds of values:

• Network returns a string of 2g/3g/4g etc.
• Hardware concurrency returns an integer for the number of cores
• Memory returns a boolean of whether you are overloaded
• Battery returns a float value . (e.g 0.75)
• Device class returns a string for light/heavy

Of these values, memory stands out as a hook where we (project authors) are making a decision about what is overloaded. For all the other hooks, we just give developers the value and let them make a decision themselves.

For consistency, we should rewrite the memory hook to just provide a value from navigator.deviceMemory and optionally provide access to performance memory data, but assume the deviceMemory value is the main thing developers are after here.

cc @anton-karlovskiy

[anton-karlovskiy]

@addyosmani
It makes sense.

1. updating memory hook with its Unit Test -- done
2. updating memory demo projects -- done
3. updating hooks/README -- done
4. local testing -- done
5. deployment again -- done
6. online testing -- done

[addyosmani]

That would be great. Thank you!