Add referer plugin

It's actually a little bit modified merge of
https://github.com/krautcomputing/count-von-count/commit/4793fb38e4da8e49d69ac17a921401651e3404aa
and
https://github.com/krautcomputing/count-von-count/commit/d842ccdf49efe9753355752bfacb93f686b9dddd
Update vim swap file pattern
Update config
remove debugger

Merge of
https://github.com/krautcomputing/count-von-count/commit/d1b59b6e7c25593fc8ea8828b35a85a04d8fd046?diff=split
remove spork

Merge of
https://github.com/krautcomputing/count-von-count/commit/4a240587372e0de90e35eaa2b920db1952d4bff1
clean up specs and dependencies

Merge of
https://github.com/krautcomputing/count-von-count/commit/79721c163d075d0338427634854f88ff7ea4db3b?diff=unified
Config file: "id" is treated as "count": substitution is possible
Object name (actually, it's id/key prefix) is treated as "count" and "id": substitutions are possible
Time is rounded to 30m intervals
Redis counter functions return their result
Add mean() custom function, add config example using mean for downsampling