Added IgnoreTrailingSeparatorChar property to fix issue of trailing separator character at the end of the line

Consider following file:
```
column1;column2;column3;
```
Though it's not a canonical representation of CSV file, that trailing separator at the end of the line breaks file reading: reader considers one more ```null``` column, so ```ContainsKey()``` method on ```null``` value throws an exception.  
I added ```IgnoreTrailingSeparatorChar``` property to ```CsvFileDescription```, so reader ignores trailing separator character at the end of the line.

I'm not exactly sure but maybe it should be implemented as a regular feature without additional property to ```CsvFileDescription```. 

Thanks,
Roman