Added awk script for producing names from enums.

- In your .h file: #include "ENUM_NAME_enum.h"
- In your .c file: #include "ENUM_NAME_names.c" (yes include).
- Create a ENUM_NAME.se file:
  strenum ENUM_NAME
    ID_0 expr_0
    ID_1 expr_1
    ...
  endenum

  - expr_k's are optional
  - You may use "//" comments in the normal fashion.
- run awk -f se.awk < ENUM_NAME.se > ENUM_NAME_enum.h
  - ENUM_NAME_enum.h contains
    enum ENUM_NAME {
      ID_0 = expr_0,
      ID_1 = expr_1,
      ...
    };

    - if expr_k not given in .se file then no "= expr_k" will be written to
      ENUM_NAME_enum.h
  - ENUM_NAME_names.c contains a function:
      char *ENUM_NAME_to_name(int n)
    which can be called to convert one of the enumerated values to a
    constant character string.
- NOTE: This has only been tested on VM_RETCODE enumerated types used by vm.h and
        vm.c