Usage of both parser and generator about arduinojson

[bblanchon]

My personal advice is to put the using statement in the function scope.
But this will only work if you use the parser and the generator in different functions.

Otherwise, you can simply use the namespace ArduinoJson and then prefix the names with Parser:: or Generator::.

Please also look at this blog post.

[bblanchon]

I added an explanation in JsonGenerator/README.md and JsonParser/README.md:

Having a namespace conflict?

To be able to use both ArduinoJson::Generator and ArduinoJson::Parser in the same file, you need to do one of the followings:

• Put the using statements into different functions
• using namespace ArduinoJson;, then prefix the type names by Generator:: or Parser::
• Create aliases for the namespaces or the types (C++11 only)