Add more examples to README

[d99kris]

Proposed examples to be added:

1. List supported datatypes for Get/Set-functions, i.e. int, long, long long, unsigned, unsigned long, unsigned long long, float, double, long double, char, std::string.
2. How do construct Document from a std::string containing CSV data, using stringstream - see Add support for access original data for advanced process and load csv from string. #25
3. Examples showing reading three common CSV file types (with table illustrating file content); no headers, column headers, both column and row headers.