STY: Style fixes for better readability (QuantEcon#629)

RELEASE: Preparation for v0.5.2 (QuantEcon#593)

* preparation for v0.5.2

* update README with changes

RELEASE: Setup for v0.5.1 (QuantEcon#586)

RELEASE: Setup for Release 0.5.0 (QuantEcon#578)

* update version to 0.5.0

* Add README

update version for new release (QuantEcon#555)

Release of version 0.4.7 (QuantEcon#534)

update version to 0.4.6 (QuantEcon#520)

* update version to 0.4.6

* updates change notes

Release of version 0.4.5

Release of version 0.4.4

Release of version 0.4.3