posts: Add archived posts from acm-ucr/acm-phoenix

I converted all the old articles from acm-ucr/acm-phoenix's database to the markdown format jekyll expects.

Some oddities (that can be fixed):
- what you now categorize as "general meeting" used to just be "general." You(I) could just run `sed` to fix that.
- there is no special jekyll handler/template for files under the archives/ folder so they just all show up on the front page.

Not sure if anyone cares about the former, but for the latter, it seems that we can revisit this when acm-ucr/acm-phoenix-static#5 is resolved.

This closes acm-ucr/acm-phoenix-static#8