Add documentation and core BASIC language functions
- Add SET_SCHEDULE.md and TEMPLATE_VARIABLES.md documentation
- Implement array functions (CONTAINS, PUSH/POP, SLICE, SORT, UNIQUE)
- Implement math functions module structure
- Implement datetime functions module structure
- Implement validation functions (ISNULL, ISEMPTY, VAL, STR, TYPEOF)
- Implement error handling functions (THROW, ERROR, ASSERT)
- Add CRM lead scoring keywords (SCORE_LEAD, AI_SCORE_LEAD)
- Add messaging keywords (SEND_TEMPLATE, CREATE_TEMPLATE)