ACL trend survey

Requirements

Configure year and journal in crawler/crawler/settings.py. (Haven't tried crawling other proceedings/journals than ACL though)
```
  $ cd crawler
  $ scrapy crawl acl -o items.csv -t csv
  $ scrapy crawl acl -o items.json -t json
```
Be careful of running the code twice because the json file gets appended, rather than overwritten.

$ python count.py