Generalized SEIR Epidemic Model (fitting and computation)

Updates:

• Added a folder Documentation.pdf that display the examples and documentation in a pdf format
• Examples updated
• Deleted the example with French regions, since the data were no longer updated
• Added an optional parameter in datetime, which improve the code performance for users in e.g. China (cf. Issue Time error #13)

Full description of the code and documentation available at:

• https://se.mathworks.com/matlabcentral/fileexchange/74545-generalized-seir-epidemic-model-fitting-and-computation

• https://github.com/ECheynet/SEIR