Implement equals in ColumnTypes.

[AliLozano]

In Column the equals is:

   override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other !is Column<*>) return false
        if (!super.equals(other)) return false

        if (table != other.table) return false
        if (name != other.name) return false
        if (columnType != other.columnType) return false

        return true
    `}`

It compares column type, but column types are only compared by reference because they don't implement equals and always return false inclusive when they are the same.

[Tapac]

@AliLozano, thank you for a PR, but looks like you forgot to check nullable field of ColumnType

[AliLozano]

You're right @Tapac thanks, I've added it.

[spand]

hashcode seems to be missing.

Joshua Bloch says on Effective Java

You must override hashCode() in every class that overrides equals(). Failure to do so will result in a violation of the general contract for Object.hashCode(), which will prevent your class from functioning properly in conjunction with all hash-based collections, including HashMap, HashSet, and Hashtable.

[Tapac]

@spand , nice point. I'll fix it master. It's easy to forget such esential things when you live in world of data classes for too long :D