Made it so it won't double post + some other stuff.

[zegevlier]

I did 4 things in this PR:

• changed NUMBER_DAYS_FORPOSTTOBE_OLD to NUMBER_DAYS_FORPOSTTO_BE_OLD
• Made it so that the bot won't post something again if it has posted it within the last 20 posts. This is to make sure it doesn't post the same thing twice.
• I changed the way to get the amount of second since the Unix epoch. The way it was done was to be avoided (it isn't officially supported, though it might work), this also works.
• I changed the post deletion threshold to 0. If one user downvotes the post we can assume it said something stupid. There is no need to wait until 3 people downvote it. Reddit gives you 1 upvote so start with so it can be set to 0.