Load Pokemon from files

[manueldidonna]

Create an immutable Pokemon instance from a file which has been converted to a UByteArray. The machism is the same used by SaveData.Factory

interface Pokemon {
    interface Factory {
        /**
         * Create a [Pokemon] instance from an array of bytes 
         * or null it it doesn't rapresent a valid pokemon.

         */
        fun create(data: UByteArray, position: Position): Pokemon?
    }
}

Related to #1