Mark Old Docs as DEPRECATED

[nothingismagick]

Many users have accidentally stumbled onto older versions of the docs without realizing that many of the methods described just won't work anymore. We should look into a way to remind them that they are looking at outdated reference material and guide them to the newest docs.

[disarticulate]

Perhaps header tags like:

Installation [0.15+]

Vuejs docs tend to have one source, and updated headings for the API:
https://vuejs.org/v2/api/#warnHandler