Implementation of small client

[Hu6li]

This pull request addresses issue #27

Implementing a simple client for cloudspanner/postgres
Currently it is only possible to query and print samples formatted as json
This can of course be extended into a more powerful client.

Please let me know what you think

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[meeehow]

Hi @Hu6li, thank you for this pull request! Would it be possible to decouple the server code from the client code? What I mean is to keep all the code that the client uses in the "main" package, under /client

[Hu6li]

Hi @meeehow sure this is possible.
Is your intention to run the client as a complete independent program?
This would probably mean having some code redundancy overall as we wouldn't reuse parts of the already existing interfaces and create new/separate ones.

[meeehow]

@Hu6li Yes, the idea would be to have the server and the client code independent of each other. IIUC for this PR there shouldn't be much too of code redundancy, you'd just need to create the cloudspanner and postgres clients (and potentially structs).

[meeehow]

Looks good, could you just fix the issue below?

"don't use underscores in Go names; var file_output should be fileOutput"