When computing the size of the directory structures, take care about the size
taken by the RR/SUSP fields. Also, cache that size, otherwise we need to do
this computation several times and it is ugly, because the CE entries need to
know where the Continuation Area will be stored.
This only adds the tree creation functions, no sorting and name mangling
yet. Only plain ECMA-119 supported for now, nor RR, relaxed
restrictions, etc..
This also adds a little test program.