Integrate API and add TOC into README

[thejonan]

It will be better to have the API reference and a Table of Content inside the README.md.

The most efficient steps seem to be:

• Have the current content of README.md as a separate file (a.k.a README.base.md), with {{TOC}} and {{API}} placeholders.
• Utilize the markdown-toc library to generate the TOC.
• A simple string.replace() should be fine for this content insertion, because it is not complicated - no need to a dependency to yet another library just for that purpose.
• It would be better to have the generate API content (which is currently dumped into API.md file) be merged into README.md before the TOC generation, in order to have it's labels in as well.
• Modify the gulp's doc task in order to have this process properly handled.