Refactored documentation generation, removed generated docs from git

It does not make sense to keep generated documentation in git, hence I
refactored it a bit. The source code archive for releases should now also
be more than 50% smaller according to one test. And they no longer need to be
maintained separately.

The documentation is now built by default, but this behavior can be disabled or
restricted using the the GENERATE_(HANDBOOK|HOWTO)_(HTML|PDF)(_LANGUAGES)? cache
options.

The generated documentation is stored below ${CMAKE_CURRENT_BINARY_DIR}/docs
using a <doc>/<lang>/<format>/ substructure for directories.

The ${CMAKE_CURRENT_SOURCE_DIR}/docs/<doc> folders now only contains the English
originals with docbook sources in ${CMAKE_CURRENT_SOURCE_DIR}/docs/<doc>/docbook
and images in ${CMAKE_CURRENT_SOURCE_DIR}/docs/<doc>/images.

.travis.yml

@@ -52,6 +52,12 @@ addons:
       - qt512webengine
       - qt512xmlpatterns
       - qt512tools
+      # Documentation:
+      - fop
+      - po4a
+      - xsltproc
+      - docbook-xml
+      - docbook-xsl
   coverity_scan:
     project:
       name: "bibletime/bibletime"

README.md

@@ -19,15 +19,37 @@ The following requirements are needed only if you want to develop BibleTime.
 
 ### DOCUMENTATION GENERATION REQUIREMENTS (OPTIONAL)
  - po4a
- - xsltproc, docbook-xml, docbook-xsl
-
-These packages are used by BT committers to prepare
-the documentation for the Handbook, Howto and the
-website.  This tool set can be used by translators to
-generate, test and validate their work.
-There is no need to rely on these packages to bundle
-BibleTime for distribution as the compiled documentation
-is in the source tree ready for installation.
+ - xsltproc
+ - docbook-xsl
+ - docbook-xml
+ - fop (for PDF generation)
+
+These packages are only used by the build system when document generation and
+installation is enabled. By default, all translations of the handbook and howto
+documents are generated and installed. This can be changed using the following
+options to CMake:
+
+ * GENERATE_HANDBOOK_HTML - whether to generate and install the HTML handbook
+ * GENERATE_HANDBOOK_HTML_LANGUAGES
+       - list of language codes to use for HTML handbook, or empty for all
+         languages
+ * GENERATE_HANDBOOK_PDF - whether to generate and install the PDF handbook
+ * GENERATE_HANDBOOK_PDF_LANGUAGES
+       - list of language codes to use for PDF handbook, or empty for all
+         languages
+ * GENERATE_HOWTO_HTML - whether to generate and install the HTML howto
+ * GENERATE_HOWTO_HTML_LANGUAGES
+       - list of language codes to use for HTML howto, or empty for all
+         languages
+ * GENERATE_HOWTO_PDF - whether to generate and install the PDF howto
+ * GENERATE_HOWTO_PDF_LANGUAGES
+       - list of language codes to use for PDF howto, or empty for all languages
+
+For example, passing `-DGENERATE-HOWTO_HTML_LANGUAGES=en;et` to the cmake
+command to restricts generation and installation of howto HTML versions to the
+English and Estonian translations only, and `-DGENERATE_HOWTO_PDF=OFF` disables
+generation of the howto in PDF format.
+
 
 ### PROCEDURE