Add documentation, move files to a proper place and avoid memory leaks.
Make it work with most kind of texts, and allow backgrounds too.

openSUSE sets that option to ON.

Fixes #3420.

  * Combine client and server man pages.
  * Update unit test options and available databases in man page.
  * Add `--worldname` to man page.
  * Fix a bunch of places where `"Minetest"` was used directly instead of `PROJECT_NAME`.
  * Disable server build by default on all operating systems.
  * Make `ENABLE_FREETYPE` not fail if FreeType isn't found.
  * Enable LevelDB, Redis, and FreeType detection by default.
  * Remove the `VERSION_PATCH_ORIG` hack.
  * Add option to search for and use system JSONCPP.
  * Remove broken LuaJIT version detection.
  * Rename `DISABLE_LUAJIT` to `ENABLE_LUAJIT`.
  * Rename `minetest_*` variables in `version.{h,cpp}` to `g_*`.
  * Clean up style of CMake files.

Minetest fails to build on GNU/Hurd due to a name clash with OSX/Apple,
both are defining the __MACH__ keyword. This commit fixes the issue.

because cmake is unable to parse it's own lists properly

This can solve numerous problems such as:
http://www.cmake.org/Bug/view.php?id=13959
http://www.cmake.org/Bug/view.php?id=14601

If pkg-config or freetype2.pc is not found, then fall back to the
FindFreetype.cmake module logic.

Restrict to UNIX since I only tested it here.