You can deactivate the account on your own. As a note, once you deactivate the account there is no turning back.
In order to deactivate the account you need to do the following:
Click on your account profile.
Navigate to "edit profile" at the top of the page directly under your name.
Once you are in the edit profile section scroll all the way to the bottom and click "deactivate account" (the link is in red).
Again, once you deactivate there is no going back. I would strongly suggest against this. That being said I am sure you have your reasons. Good luck on your future endeavors.
Deactivation isn't the main issue on its own, unless this whipes all my posts away too?
IF not, can a webmaster or mod intervene and do it? Due to the... not so great way the edit pages work, it would be far too much effort manually.
Deactivation doesn't necessarily wipe out all posts. However, when you do deactivate it changes the name of the account to "deactivated-123xyz" all of your posts are essentially attributed to "deactivated-123xyz." We can go through the process of nuking the account after you deactivate but that is not entirely necessary as there would be no link (aside from the mod note visible to staff and mods only) between those messages and your old account.