Various Updates

I finally got some files accepted using the `IBANPayment`s. It's been more work than expected, so the PR has become quite large.

I'd really like to have this thing released to rubygems, so please tell me what you think.

Changes:
* fixes https://github.com/phuesler/payment_dta/issues/2 (calculate entry_sequence_number)
* ruby 1.9/2.0 compatible
* add [SimpleCov](https://github.com/colszowka/simplecov)
* output to a string
* use swift convention for amount formatting
* use BigDecimal for calculating the TotalRecord sum to prevent rounding errors
* truncate long input for beneficiary_address_line[1-4]
* convert characters in the `@data`-hash getter, before building the final record to get the correct record-lengths