Prototype: Add defaulter support

[sttts]

We plan to use go-openapi for CustomResourceDefinition validation in Kubernetes (compare kubernetes/community#708). For that will need support for default values. This is a prototype to integrate this into go-openapi.

[casualjim]

I haven't forgotten this I've just been very busy with work stuff (ironically: related to kubernetes) and haven't have been able to properly grok this PR.
Will try to get to it in the next 10 days

[casualjim]

could you update this?

[sttts]

@casualjim just returned from vacation today. Will update after having catched up with mails.

[sttts]

@casualjim rebased and simplified a lot

[codecov]

Codecov Report

Merging #27 into master will increase coverage by 0.31%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #27      +/-   ##
==========================================
+ Coverage   83.71%   84.03%   +0.31%     
==========================================
  Files          10       10              
  Lines        1363     1384      +21     
==========================================
+ Hits         1141     1163      +22     
+ Misses        182      180       -2     
- Partials       40       41       +1

Impacted Files	Coverage Δ
schema.go	78.86% <ø> (-0.34%)	⬇️
schema_props.go	96.07% <100%> (+0.42%)	⬆️
object_validator.go	89.47% <100%> (-1.84%)	⬇️
result.go	95.83% <100%> (+18.05%)	⬆️

---

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[codecov]

Codecov Report

Merging #27 into master will increase coverage by 0.31%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #27      +/-   ##
==========================================
+ Coverage   83.71%   84.03%   +0.31%     
==========================================
  Files          10       10              
  Lines        1363     1384      +21     
==========================================
+ Hits         1141     1163      +22     
+ Misses        182      180       -2     
- Partials       40       41       +1

Impacted Files	Coverage Δ
schema.go	78.86% <ø> (-0.34%)	⬇️
object_validator.go	89.47% <100%> (-1.84%)	⬇️
result.go	95.83% <100%> (+18.05%)	⬆️
schema_props.go	96.07% <100%> (+0.42%)	⬆️

---

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 035dcd7...f358b0e. Read the comment docs.