Markdown formatting changes

Improving Markdown rendering on Github.

I noticed that the bulleted lists weren't indenting correctly. Fixing that led to some other (relatively minor) formatting changes.

Overall result: Slightly better documentation rendering and user experience.
Merge pull request #64 from vmbrasseur/readme-formatting

Markdown formatting changes in README.md
Merge pull request #65 from wikimedia/wikimedia

Adding support for integer unix timestamp in JsonStringMessageDecoder
Automatically converting to millisecond timestamp if the value is large enough

Change-Id: I558f11db2e662fb35428a3a561e544dd0b13989e