The algorithm to compute the derived property should use EAW more

[kojiishi]

This issue is a continuation of kojiishi/unicode-auto-spacing#16, originally raised by @asmusf.

[kojiishi]

@asmusf The algorithm to compute the property was adjusted to:

1. Add by scripts and script_extensions.
2. Remove by EAW.

In other words, the algorithm is an intersection of scripts and EAW.

Does it make clear that EAW plays one of the primary roles for this property?

[kojiishi]

With #768, ea=N|Na are exlucded from the W set, unless their script is one of CJK.

The current algorithm to compute the property is here. It's in Python with a library, but I hope it's readable without prior knowledge.