Add ipv4 observable and validation

- Now store ipv4 in an Ipv4Observable object
- Validation requires the ipv4 be an IP::V4 object (provided by
  ruby-ip), with a prefix length of 32 bits.
Update specs to reflect ipv4 model changes

- Now using Ipv4Observable objects in Ipv4ObservableCollections
Ensure that none of our feeds have errors

- When running describe_parsing_the_file, ensure that none of the parsed
  records had errors.
Fix sigmaproject:spyware

- Was not properly filtering for host IP addresses.
Fix sigmaproject:webexploit

- Was not properly filtering for host IP addresses.
Return proper events/records
Remove redundant check for missed records
Fix missed records for ET:openbadlist
Fix issue with sigmaproject:atma

- Was not filtering IP addresses properly
Update changelog
Merge pull request #100 from justfalter/validate_ipv4_fqdn

Validate IPv4, update model, various feed fixes