v2beta-json: Add optimized method for dumping any value to JSON (#41)

[seandstewart]

This addresses #41

Features:

• Optional lazy evaluation of fields when serializing with typic.primitive or MyObj.primitive
• New high-level typic.tojson and MyObj.tojson methods for fast, easy serialization.
• New json extra for automatically installing typical's json serializer of choice.

[codecov]

Codecov Report

Merging #44 into master will decrease coverage by 0.1%.
The diff coverage is 97.61%.

@@            Coverage Diff             @@
##           master      #44      +/-   ##
==========================================
- Coverage   98.66%   98.56%   -0.11%     
==========================================
  Files          34       35       +1     
  Lines        2852     2998     +146     
==========================================
+ Hits         2814     2955     +141     
- Misses         38       43       +5

Flag	Coverage Δ
#unittests	98.56% <97.61%> (-0.11%)	⬇️

Impacted Files	Coverage Δ
typic/util.py	96.26% <100%> (-0.17%)	⬇️
typic/api.py	96.49% <100%> (+0.02%)	⬆️
typic/serde/resolver.py	97.12% <100%> (+0.25%)	⬆️
typic/mypy.py	96.02% <100%> (+0.34%)	⬆️
typic/serde/common.py	100% <100%> (ø)	⬆️
typic/ext/json.py	100% <100%> (ø)
typic/ext/schema/field.py	99.2% <80%> (-0.8%)	⬇️
typic/serde/ser.py	98.23% <97.32%> (-1.77%)	⬇️

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