Add docs-html target to CMake

Only added if Sphinx can be found.
Refs #9521

Code/Mantid/docs/CMakeLists.txt

+###############################################################################
+# Sphinx documentation
+###############################################################################
+find_package ( Sphinx )
+
+if ( SPHINX_FOUND )
+  # Fill in the config file and autogen file with build information
+  
+  # We generate a target per build type, i.e docs-html
+  set ( SPHINX_BUILD ${CMAKE_BINARY_DIR}/docs )
+  set ( BUILDER html )
+  configure_file ( runsphinx.py.in runsphinx_html.py @ONLY )
+
+  # targets
+  set ( TARGET_PREFIX docs)
+
+  # HTML target
+  add_custom_target ( ${TARGET_PREFIX}-html 
+    COMMAND ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/MantidPlot -xq runsphinx_html.py
+    COMMENT "Build Sphinx html documentation"
+  )
+
+endif ()
+
+
+###############################################################################
+# QtAssistant
+###############################################################################
 if ( APPLE )
   set ( ENABLE_QTASSISTANT False CACHE BOOL "Build qt-assistant documentation" )
 else ()

Code/Mantid/docs/runsphinx.py.in

+"""We need to run Sphinx inside MantidPlot to document the internal
+   module. This script calls the sphinx entry point with the necessary 
+   arguments
+"""
+
+__requires__ = 'Sphinx'
+import sys
+import os
+from pkg_resources import load_entry_point
+
+mantidplot = "@CMAKE_RUNTIME_OUTPUT_DIRECTORY@/MantidPlot"
+builder = "@BUILDER@"
+src_dir = "@CMAKE_CURRENT_SOURCE_DIR@/source"
+output_dir = os.path.join("@SPHINX_BUILD@", builder)
+argv = [mantidplot,'-b', builder, src_dir, output_dir]
+
+if __name__ == '__main__':
+    sys.exit(
+      load_entry_point(__requires__, 'console_scripts', 'sphinx-build')(argv)
+    )
+