OFX (v1.x) headers

Thanks for all of the work on this project.

Looking at the OFX output, it appears that the `DATA:OFXSGML` and `ENCODING:UTF-8` headers are added. What do you think of adding other common OFX headers such as:
```
OFXHEADER:100
VERSION:102
CHARSET:1252
SECURITY:NONE
COMPRESSION:NONE
OLDFILEUID:NONE
NEWFILEUID:NONE
```