* Adds the send_once command and message type, which allows a user to request a variable to be sent immediately and only once (intended to replace the var_add, var_send, var_clear idiom that is commonly used for this purpose)
* Minor refactoring of variable server internals to reduce repeated code
* Adds SIM_test_varserv to integration test to test basic variable server functionality
* Changes graphics client for SIM_billiards to use var_send_once as an example of intended use
* Add documentation for var_send_once in docs and tutorial
* Set exit_code_enabled in trick unit tests to be true by default
* Patch for failing bookworm build
Reorganized. Created a new top level include directory that will hold all of Trick's header files. Moved all of the Trick headers to this directory. Created a libexec directory that holds all of the executables that users don't need to execute directly. Changed all of the executables remaining in bin to start with "trick-". In the sim_services directories changed all source files to find the Trick headers in their new location. Since all of the include files are gone in sim_services, removed the src directories as well, moving all of the source files up a level. Moved the makefiles, docs, man, and other architecture independent files into a top level share directory. Renamed lib_${TRICK_HOST_CPU} to lib64 or lib depending on the platform we're currently on.
refs #63
