Improved compatibility with older GL versions

- Added ifdefs around functions that require a higher GL version
  than 3.0 in Framebuffer and shape drawing.
Minor documentation update
Minor update of the README file

- Updated acknowledgements.
Added a new utility script
Started release-0.31.0
Fixup of the workflow utility script
Fixup in the build system

- Disabled building of the spectra sdvanced example
  if openAL is not detected.
Multiple changes

- Updated the changelog.
- Updated the web index page.
Fixup of the git workflow utility script
Merge branch 'release-0.31.0' into develop
Update of the workflow script
Fixed a problem with MSVC in Exposed<T>
Updates of the main cmakelists.txt

- Fixed a typo.
- Refactored X11/GLX detection.
Added a missing cmake script
Minor documentation fix
Renamed a member variable in OALplus ErrorInfo
Fixup of a problem in OALplus enumerations
Initial commit of EGLplus

- Added config.hpp header.
- Added exceptions and error handling.
- Added wrapper for Display.
- Added EGL library RAII initializer.
- Added String and StrLit.
- Added macros for defining strongly typed enumerations.
- Added the StringQuery enumeration.
- Added the ColorBufferType and TransparentType enumerations.
- Added the ConfigAttrib and ConfigCaveat enumerations.
- Added the SurfaceTypeBit and RenderableTypeBit enumerations.
- Added the Configs and Config classes.
- Added Bitfield.
- Added FriendOf.
Updated the configure bash script

- Added options for forcing of GL header and context initialization library.
Multiple changes

- Added the ErrorCode enumeration.
- Changed value names in the ConfigAttrib enumeration.