Use new() method instead of having structs public

[Anders429]

Rather than having all of the different internal structs have public visibility, it may be possible to use a new() method on WordFilter to construct it instead. The new() method would need to be a const fn to be used in static context.

The input parameter would just be a fixed-size array of size N, with each element being a tuple containing the values needed for a State, which are:

• Flags - This will be an integer value after #67 is completed.
• c_transitions - This will be a closure.
• aliases - slice of 2-tuples of references.
• graphemes - slice of references.

The references may be a problem, since they reference into the array being constructed in the new() method. This may not have to be a problem though, depending on how self-referencing works in const contexts.

[Anders429]

The array-const-fn-init crate may be required to make this possible at this point. May need to experiment to see if it can be used with a const generic.

Edit: nevermind, this doesn't work with const generics :(

[Anders429]

Looks like this is going to be blocked by the const_fn_fn_ptr_basics feature becoming stable, since it is needed to allow a function pointer to appear as a const fn parameter.