Add 'prefix' function to ipaddr filter.

[mattcoley]

Final request for ipaddr filter #236.

Returns the CIDR prefix of a valid IP address. If the IP address is invalid or the prefix is not a number it will return null. Example usage:
'1.0.0.1/24'|ipaddr('prefix') would return 24.

[codecov-io]

Codecov Report

Merging #243 into master will increase coverage by 0.26%.
The diff coverage is 68.18%.

@@             Coverage Diff              @@
##             master     #243      +/-   ##
============================================
+ Coverage     71.89%   72.15%   +0.26%     
- Complexity     1392     1441      +49     
============================================
  Files           220      220              
  Lines          4365     4478     +113     
  Branches        690      728      +38     
============================================
+ Hits           3138     3231      +93     
- Misses          992     1006      +14     
- Partials        235      241       +6

Impacted Files	Coverage Δ	Complexity Δ
...a/com/hubspot/jinjava/lib/filter/IpAddrFilter.java	70.96% <68.18%> (-13.65%)	12 <6> (+4)
...m/hubspot/jinjava/lib/filter/RejectAttrFilter.java	80.76% <0%> (-19.24%)	10% <0%> (+7%)
...bspot/jinjava/lib/filter/DateTimeFormatFilter.java	100% <0%> (ø)	8% <0%> (+4%)	⬆️
...n/java/com/hubspot/jinjava/lib/tag/TagLibrary.java	82.35% <0%> (+0.53%)	8% <0%> (+3%)	⬆️
...ain/java/com/hubspot/jinjava/lib/fn/Functions.java	84.41% <0%> (+2.51%)	55% <0%> (+24%)	⬆️
...m/hubspot/jinjava/lib/filter/SelectAttrFilter.java	75% <0%> (+4.62%)	15% <0%> (+7%)	⬆️

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[boulter]

The only problem with this is that it creates more reasons to build uncacheable pages. :(

[mattcoley]

I can't see this being terribly useful on Hubspot-hosted pages. The original feature requester seems like he is using Jinjava directly.