Remove mscgen setup for now. Previously it was setup in the hope \msc command will be used in our Doxygen documentation. But since that does not happen and there is no platform-agnostic way to determine the location of the mscgen tool, it is being disabled now until our documentation really needs it.
Fix the exclude pattern to filter out the graphics backend not being used in a build.
Make Doxygen and Graphviz a prerequisite software packages when URHO3D_DOCS build option is set to true (i.e. when 'doc' target is being included as part of the default 'all' target).
Use FindHTMLHelp.cmake module to remove hardcoding of HHC.exe path.
Other changes in the commit:
- Change build option from URHO3D_BUILD_TYPE to URHO3D_LIB_TYPE. Default value is STATIC.
- Automatically add compiler definition 'URHO3D_STATIC_DEFINE' when linking with Urho3D library statically.
- Move LuaScript subsystem from Extra/ to Engine/.
- Enable FindUrho3D module to also detect Urho3D library target when the FindUrho3D module is being used internally by Urho3D project.
- Configure to build all the samples for iOS and Android platforms also when option to build samples is enabled.
- Export all the Register*Library() global functions.
- Rewrite all the tools, samples, and extras targets to link against Urho3D library.
TODOs:
- Combine engine sub-libraries into one.
- Test builds on non-Linux platforms.
