docs/core: handle these

[meowsbits]

I kind of hid them there with #60 ... they are just loosely-categorized docs taken cut-and-paste from the original README.md.

• revise them to fit core-geth better, vs. go-ethereum.
  • fix links
  • tweak cli flags/usage
  • update ./cmd/ directory information
• integrate them with http://core-geth.org somehow.

Rel #61

[ziogaschr]

Some work has been done towards this at #291. So now, we can work on the content of the Markdown pages.

[meowsbits]

Indeed. I'm going to close this since we have rather handled the docs/core, and we can create a new issue(s) for further documentation efforts as required.