Hi there!

First of all thanks for your awesome library.
I noticed that CSVReader completely ignores the delimiter (when specified on constructor) when we use ToMatrix() or ToTable().

This is due to ReadField() forcing a GuessDelimiterFromBuffer() on initialization: 
https://github.com/accord-net/framework/blob/development/Sources/Accord.IO/Csv/CsvReader.cs#L1090
https://github.com/accord-net/framework/blob/development/Sources/Accord.IO/Csv/CsvReader.cs#L1126

This GuessDelimiterFromBuffer() should not happen if delimiter was specified from constructor.

We noticed the issue because in french the double parser expects 0,12 (instead of 0.12), but reading the matrix 0,12;0,13 separates the entries according to ',' instead of specified ';'

I can make a PR on this issue if needed.