Minor fix in [histogram](https://h2r.github.io/pomdp-py/html/api/pomdp_py.representations.distribution.html#module-pomdp_py.representations.distribution.histogram) to avoid print confusion.
Improvements to documentation, in particular the [tiger tutorial](https://h2r.github.io/pomdp-py/html/examples.tiger.html).
See [change log](https://h2r.github.io/pomdp-py/html/changelog.html#version-1-3-2-04-03-2021) for details.