gnucash-docs: update to 2.6.19.

2.6.19 - 16 December 2017
        o Bug 782423 - Help 10.2. Setting Preferences is outdated #105
        o Changing text in Help to reflect changes in Preferences dialogs.
        o Translation of the german guides metafile

2.6.18 - 24 September 2017
        o The Italian Help translation, which uniquely uses a PO file, is
          frozen at commit 78cfa76 because of lack of a translator to
          maintain it.
        o Bug 120940 - Document how automatic decimal points work.
        o Begin a Russian translation of the Guide by Dimitry Mangul.
        o Some spelling corrections in the German Guide.

2.6.17 - 2 July 2017
        o Improve internationalization of the Tutorial and Concepts Guide.
o Bug 781711: Add reversing transaction definition
o Bug 781714: Add Reversing Transaction text for Help document

2.6.16 - 26 March 2017
        o Remove section "Changing the Register View" as better handled in Guide
          section 4.2
o Bug 755174 - How to handle commission when buying and selling securities
o Bug 769457 - More info re register views
o Bug 774658 - Add warning to delete lot before deleting a cap gain/loss
                transaction
o Glossary: Transactions have at least 2 splits
o Bug 777318 - Restructure Business Features Chapters.
o Bug 777287 - add tips on changing reconcile status of all transactions
                in reconcile window panes

2.6.15 - 18 December 2016
        o Bug 397135 - Hidden Accounts Show in ComboBox.
o Bug 633590 - Add a Reports Chapter to the Tutorial and
              Guide.
o Bug 743671 - Add glossary to Tutorial and Guide.
o Bug 755174 - Document using Lots to create investment
              capital gains transactions.
o Bug 770371 - Add note to documentation regarding Sort order
              options.
o Bug 775592 - General Rewrite of Guide Chapter on Multiple
              Currencies.
o Bug 775919 - Change Documentation of contributors
o Update German Translation (Mechtilde Stehmann)
o Fix resolution of screenshots.

(wiz)