Descriptive README
Cleaner code, comments, improved JSON

Uses for loop instead of while
Prints JSON array pretty_printed.
Update README.md

Woops, marketcap.php should be market_cap.php...
Changed keys as required, removed non-decimal characters
Merge branch 'master' of https://github.com/beta0x64/cmc-json
Commented data cleaning
Added example output to README.md
Added JSON syntax highlighting

Also put example into code block
Added negative sign to filter

That would have been bad!
Merge pull request #7 from beta0x64/master

Improved README, improved code, added comments