This is because it's really easy to get a name collission if compiling
Jansson as a subproject in a larger CMake project. If one project includes
several subprojects each having their own config.h, this will cause the
wrong file to be loaded.
This will simplify linking against the lib, both from the build-tree and
install-tree from other CMake projects.
CMakes find_package command uses these configs to locate the exported
targets for the library.
* Also changed so that all CMake options for the project are prepended
with JANSSON_ so that there is no ambiguity when including this as a
subdirectory in another CMake project.
- Also added better FindSphinx support so that we can detect the version and not have a fatal error if it's too old.
- Added support for building latex documentation with -DBUILD_LATEX. Off by default.
- Added suppor for building man pages with -DBUILD_MAN. On by default (unless sphins is too old to support it).
