in2csv: allowed user to change output format of csv and added --decimal-delimiter flag

When decimal separator in Windows is set to comma Excel will generate CSV with comma-separated floats and semicolon-separated fields. Sometimes external software relies on this behavior and accepts only CSVs with comma as decimal delimiter and semicolon as field delimiter for specific locale settings.

To enable csvkit users to generate CSVs for such software I added flags to change settings of output csv and also added custom flag to replace '.' in floats.