EHN: Add random action profile generator

[oyamad]

Reminder: Update random_mixed_actions once QuantEcon/QuantEcon.jl#238 is released.

[codecov-io]

Codecov Report

Merging #107 into master will increase coverage by 0.25%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
+ Coverage   68.33%   68.58%   +0.25%     
==========================================
  Files           6        6              
  Lines         499      503       +4     
==========================================
+ Hits          341      345       +4     
  Misses        158      158

Impacted Files	Coverage Δ
src/random.jl	88% <100%> (+2.28%)	⬆️

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[coveralls]

Coverage increased (+0.3%) to 68.588% when pulling 29efb32 on random_actions into d3e2067 on master.