Context management

• sgs_CreateEngine - create scripting engine context
• sgs_CreateEngineExt - create scripting engine context and pass a custom memory function
• sgs_DestroyEngine - validate memory statistics and destroy engine context
• sgs_RootContext - find the root context
• sgs_ForkState - create a duplicate of the execution state
• sgs_ReleaseState - release an execution state
• sgs_PauseState - suspends the execution state
• sgs_ResumeStateRet - resumes the execution state, retrieves number of return values
• sgs_ResumeStateExp - resumes the execution state, returns the specified number of return values
• sgs_ResumeState - resumes the execution state without passing or receiving anything
• sgs_CreateSubthread - creates a thread (managed coroutine) with a starting function
• sgs_ProcessSubthreads - processes all subthread belonging to this state
• sgs_EventState - sets the event state
• sgs_EndOn - associates or detaches the event from thread end set
• sgs_DefaultMemFunc - example memory management callback
• sgs_Get(Err)OutputFunc - return the current output callback and its user data pointer
• sgs_Set(Err)OutputFunc - set the output callback and its user data pointer
• sgs_GetMsgFunc - return the current messaging callback and its user data pointer
• sgs_SetMsgFunc - set the messaging callback and its user data pointer
• sgs_GetScriptFSFunc - return the current virtual file system callback and its user data pointer
• sgs_SetScriptFSFunc - set the virtual file system callback and its user data pointer
• sgs_StdScriptFSFunc - default virtual file system function
• sgs_Cntl - set and/or retrieve various states in the system