Feature: Add CIDR format

[kenjones-cisco]

Adds CIDR format and validation that work for IPv4 and IPv6.

• Code formatted using goimports.
• Lint fixes based on output from golangci-lint that do not impact the exported names. Adds exclude for lint errors that requires a change to the exported names.
• Dependency updated using go mod tidy

[codecov[bot]]

Codecov Report

Merging #48 into master will decrease coverage by 0.06%. The diff coverage is 97.12%.

@@            Coverage Diff             @@
##           master      #48      +/-   ##
==========================================
- Coverage   89.33%   89.26%   -0.07%     
==========================================
  Files          10       10              
  Lines        1632     1668      +36     
==========================================
+ Hits         1458     1489      +31     
- Misses        145      149       +4     
- Partials       29       30       +1

Impacted Files	Coverage Δ
format.go	73.91% <100%> (+0.32%)	:arrow_up:
time.go	96.66% <100%> (-0.04%)	:arrow_down:
date.go	95.83% <100%> (-0.06%)	:arrow_down:
bson.go	77.19% <100%> (-0.4%)	:arrow_down:
duration.go	96.42% <100%> (-0.05%)	:arrow_down:
conv/default.go	66.66% <66.66%> (ø)	:arrow_up:
default.go	93.52% <97.94%> (-0.09%)	:arrow_down:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update bb51295...2dbb59a. Read the comment docs.

[kenjones-cisco]

@casualjim @fredbi Any feedback?

[fredbi]

Thanks @kenjones-cisco