Change linked version of document

[anselor]

I think always linking to latest from master is causing confusion.

A couple ways to go:

1. do development on a dev/unstable branch and only update master with each release
2. Change the documentation link to always link to latest stable. instead of latest master.

[anselor]

@tleonhardt @kmvanbrunt

[tleonhardt]

I think the better approach is changing the documentation to by default point to the latest stable.

[kmvanbrunt]

I already changed the About section of our github page to link to 1.5.0 docs.
But Todd is right. Our documentation is linking to the latest docs.

[tleonhardt]

I changed the Advanced Settings for our project on readthedocs.org and the Default version is now the stable one.