Clean up examples directory

[Pessimistress]

• Remove main example
• Move examples/data to examples/.data, load large data files from CDN

[coveralls]

Coverage remained the same at 39.098% when pulling 2f3b24b on x/main-example into 439e7ec on master.

[xintongxia]

• Remove main example
• Move examples/data to examples/.data, load large data files from CDN

what can we benefit from moving examples/data to examples/.data?

[Pessimistress]

what can we benefit from moving examples/data to examples/.data?

I want each directory under examples/ to be a standalone project. data is just some shared JSON files.

[ibgreen]

Nit:

I find hidden files ('.' files) to be bit frustrating, it can send users on a wild goose chase figuring out where things are.

Of course I understand and agree with the intention here, just want to encourage thinking of alternatives in the background.