Vortex library context.
This object allows to store the library status into a single reference, representing an independent execution context.
Its normal usage is to create a context variable using vortex_ctx_new and then start an execution context by calling to vortex_init_ctx. This makes the library to start its operation.
Once finished, a call to stop the context is required: vortex_exit_ctx followed by a call to vortex_ctx_free.
The following two functions are deprecated and will disapear in next releases: vortex_ctx_get and vortex_ctx_set.