Lazy loading improvements

[gunnsth]

Addresses #130

• Removed redundancy regarding resolving references in the reader
• Simplified resolving objects in the writer - Only one call to core.ResolveReferencesDeep and using traversal cache to avoid repetition.
• Fixes various issues
• Also merged in master to get updated version etc

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This change is 

[codecov]

Codecov Report

Merging #131 into development will decrease coverage by 0.04%.
The diff coverage is 72.22%.

@@               Coverage Diff               @@
##           development     #131      +/-   ##
===============================================
- Coverage        56.24%   56.19%   -0.05%     
===============================================
  Files              187      187              
  Lines            33668    33614      -54     
===============================================
- Hits             18936    18890      -46     
  Misses           12305    12305              
+ Partials          2427     2419       -8

Impacted Files	Coverage Δ
core/primitives.go	78.15% <100%> (ø)	⬆️
model/reader.go	44.7% <100%> (-4.71%)	⬇️
model/resources.go	58.7% <100%> (ø)	⬆️
model/page.go	52.23% <50%> (ø)	⬆️
model/writer.go	75.67% <69.23%> (+0.25%)	⬆️
core/utils.go	38.62% <0%> (-0.86%)	⬇️

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