Avoid errors if configuration is missing
Avoid errors if configuration is missing

Default configuration is used:

```yaml
archive_generator:
  per_page: 0
  yearly: false
  monthly: false
```

Fixes #3.

Built from 29fa9127fc231d14eb2cf5b2969366da7fd0faab.

ahaasler/hexo-theme-colos,ahaasler/hexo-theme-colos