CoralVM-C: Added two more config flags

These flags should be generated by some automated tool in much later releases of Coral, like `make`.
CoralVM-C: Added include of stdlib.h and stddef.h to coral/coral.h
CoralVM-C: Added include of stdbool.h, stdlib.h and stddef.h to coral/string_table.h
CoralVM-C: Implemented string table lookup