Added new variable paymenttypecode.

Hi,
My name is Geena. Found your library very useful in generating nacha files. I have made a small update to make the paymenttypecode as a variable. Here is a summary of what i have done.
Added new variable paymenttypecode. default it to 'S' for single entry payment.
Added a function to setPaymentTypeCode
Edited createDetailRecord - Changed field 9(WEB type detail record) to take value from the variable

Request you to merge it to the master if you find it appropriate. 
Once again thank you for the library.