[eigen_II] Minor Issues

[HumphreyYang]

This issue relates to my edits in QuantEcon/lecture-intro.zh-cn#156:

1. In https://intro.quantecon.org/eigen_II.html#primitive-matrices, we have "$A$ is primitive since $A^k$ is everywhere nonnegative", which might be "$A^k$ is everywhere positive" given the definiton of primitive matrices.
2. In https://intro.quantecon.org/eigen_II.html#example-2-connection-to-markov-chains, I think "Hamilton matrix“ refers to mc_eg2 instead of Hamiltonian matrix since it is not symmetric.

[Nanakjoth]

Hey @HumphreyYang
I just submitted a small fix for #576 — I made the definition of the primitive matrix a bit clearer and corrected Hamilton matrix label issue. Hope that helps! Let me know if you need any further changes.