Move doc build out of build step

[ericelliott]

Build runs before unit tests, which means that every time you want to run your unit tests to see if everything works, you have to wait for the docs to search the directory hierarchy and generate the TOC -- a time-consuming process that gets in the way of development.

A possible solution is to move the doc build into the prepublish step.

Expected

Doc build should not slow down unit test runs.

Actual

Users currently have to wait for a time consuming doc build before they can see the results of the unit tests.

[nkbt]

1. You don't need to run build before test. It is not required.

   "test": "babel-node `npm bin`/blue-tape ./test/**/*-test.js",

2. Docs generation is quite useless in prepublish since it modifies files that we want to commit to repo. We don't care much about readme in the npm tgz package.

[ericelliott]

:+1: