Support int32

[rauljordan]

This resolves #66 and adds full support for int32 fields as ssz-able basic types

[codecov]

Codecov Report

Merging #67 into master will increase coverage by 0.4%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master      #67     +/-   ##
=========================================
+ Coverage   72.48%   72.89%   +0.4%     
=========================================
  Files          11       11             
  Lines        1065     1081     +16     
=========================================
+ Hits          772      788     +16     
  Misses        183      183             
  Partials      110      110

Impacted Files	Coverage Δ
types/determine_size.go	80% <100%> (+0.17%)	⬆️
deep_equal.go	60.52% <100%> (+1.06%)	⬆️
types/basic.go	86.11% <100%> (+1.37%)	⬆️

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[nisdas]

@rauljordan could you add one more testcase with a struct with a int32 field.