Added the ability to parse commands as well as expressions.

Added basic PRINT and REM commands.
Added solver tests which had been around for a while and not committed.
All execution is still immediate mode.

tests/basic_tokenizer.c

@@ -4,11 +4,10 @@
 #include <stdio.h>
 
 char *_tokenize(char *ptr, char *token);
-char *_token_get(void);
 
 #define assert_token_value(str, val, ret_null, ret_neq) \
     ptr = _tokenize(str, BASIC_TOKENIZER_TOKENS); \
-    value = _token_get(); \
+    value = tokenizer_token(); \
     if ( ptr == NULL ) return ret_null; \
     rc = strcmp(value, val); \
     printf("(%s) => (value) == (val) ? : (%s) == (%s) %d\n", str, value, val, rc); \