Design PlantMeteo.jl organization of routines and code

[thomasarsouze]

Organization of the src directory.

[thomasarsouze]

First proposed organization of the sources of the packages

. src/
|-- PlantMeteo.jl : Module declaration and all imports / using / using / export  
|-- io : Reading and writing a meteo file (`.csv`)
     |-- read_meteo.jl : reading a meteo `.csv` file
     |-- write_meteo.jl : writing a meteo `.csv` file (after possible calculation, time aggregation, etc...)
|-- meteo : 
     |-- calculations.jl : weather and sun position related calculations
     |-- meteo.jl : functions used to generate the meteo data with desired variables and at desired frequency