Move Accounting Guide into OFBiz Asciidoc Framework

This is a general umbrella task for the creation and migration of all accounting related information and documentation into the OFBiz asciidoc documentation framework.

Subtasks will be created for each area where documentation needs to be created. An initial list is as follows:

1. accounting.adoc (already created - may create an issue to track any additional work_
2. acc-intro.adoc
3. acc-agreements.adoc
4. acc-tax-authorities.adoc
5. acc-invoices.adoc
6. acc-billing-accounts.adoc
7. acc-payments.adoc
8. acc-payment-gateway.adoc
9. acc-financial-accounts.adoc
10. acc-global-settings.adoc
11. acc-glossary.adoc