Log Message:
gnucash-docs: update to 3.0.

 3.0    - 1 April 2018
        o Correct field format in python-import-fields.
        o German translation of Transactions chapter.
        o Bug 122895 - general ledger should be named journal
        o Bug 634181 - Inserting Part designations overall
        o Bug 608098 - Document Transaction Rpt, including how to handle splits
        o Clarify that creating a postponed SX will use the original date.
        o Remove 'Remainder To' from loan assistant page 2.
        o Bug 760407 - Note account separator isn't always a colon.
        o Update partial date entry documentation based on new default behaviour
        o Bug 762088 - Remove Section 9.4.3 From Guide
        o New Russian translation o fthe guide.
        o Fix chm mapfile target and cleanfiles.
             The mapfile target would fail if the directory was already built,
             apparently not recognizing that its target was complete.
             Cleanfiles was missing several build targets.
        o New Transaction Report section in Guide
        o Replace some screenshots with new ones reflecting Gtk3.