v0.16.4

QuantEcon v0.16.4

Diff since v0.16.3

Closed issues:

• strange indexing bug with Kalman smoothing example (#234)
• quad.jl + qnwbeta (#263)
• Fix test failure in test_markov_approx.jl (#273)
• Fix deprecation warning with freqz (#276)

Merged pull requests:

• Replace LightGraphs by Graphs, fix deprecations, update compat (#271) (@greimel)
• replace Travis CI by Github Actions (#272) (@greimel)
• Fix broken test on julia 1.7+ (#274) (@greimel)