Improved NetCDF4/PCRaster outputs module

• Outputs module refactored to be more efficient and modular.
• New option "OutputMapsChunks" added, allowing to write steps in chunks in the NetCDF4 file. The option "OutputMapsChunks" requires as input a positive integer number X, meaning that the code will dump outputs to disk every X steps (default value = 1).
• New option "OutputMapsDataType" added, allowing to choose the output maps data type between float64 and float32 (can be used to save space in output maps).
• Added support to flipped input static maps and meteo maps
• The Lisflood OS version number is now recorded in the metadata of the NetCDF4 files. Institution and author metadata are updated according to the version of Lisflood used to generate the output files.
• Flags to check the maps: now lisflood command can be executed to check the correctness of input maps before running the model. The option -c is available as an additional command line argument (e.g. "lisflood settings.xml -c") and generates the table of all the input maps specified in the input xml file. The table will show name of the map, the file path (or single value of the variable), the number of non missing values (nonMV) and missing values (MV) after the comparison with the mask map and LDD map, minimum, maximum and average values for each map. In case any map have missing values, a warning will be issued on screen.
• The "ReportSteps" option now support formulas. The "ReportSteps" option available in XML file can be used to customize the output frequency of the model state variables. The desired time steps can be specified by using ranges, formulas and parameters as indicated in the documentation here: https://ec-jrc.github.io/lisflood-code/3_step3_preparing-setting-file. Note that this option only impacts the output frequency of the model state variables (activated by the "repStateMaps" option), not to the auxiliary variables. The full list of the affected variables is here: https://ec-jrc.github.io/lisflood-code/4_annex_state-variables/
• Lisflood OS User Guide documentation is now included into the same repository of the Lisflood software into the "docs" folder: in this way the documentation will be up to date with the corresponding lisflood release and users can access to it offline. The documentation files are written in Markdown (MD) format and are visible using a Markdown viewer locally (available on most IDE like Visual Studio, Notepad++, etc...). The documentation can be also rendered locally as a localhost website using Jekyll and Ruby.