add support for indicator and categorical input distributions in JPC format

[guyvdbroeck]

No description provided.

[codecov]

Codecov Report

Merging #111 (ee6a0ce) into master (4eb2931) will increase coverage by 0.98%.
The diff coverage is 94.11%.

@@            Coverage Diff             @@
##           master     #111      +/-   ##
==========================================
+ Coverage   45.81%   46.80%   +0.98%     
==========================================
  Files          17       17              
  Lines        1362     1391      +29     
==========================================
+ Hits          624      651      +27     
- Misses        738      740       +2     

Impacted Files	Coverage Δ
src/abstract_nodes.jl	86.95% <ø> (ø)
src/plain_nodes.jl	86.11% <0.00%> (-2.47%)	⬇️
src/io/jpc_io.jl	99.00% <96.55%> (-1.00%)	⬇️
src/input_distributions.jl	47.76% <100.00%> (+2.44%)	⬆️

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[khosravipasha]

Looks good, and seesm to be easy to support other potential node types later.