Phase 2: variables, arrays, program execution, and control flow

Add variable storage (scalar and array), program line storage with
RUN/LIST/NEW, and full control flow: FOR/NEXT, GOTO, GOSUB/RETURN,
IF/THEN/ELSE, WHILE/WEND, ON GOTO/GOSUB, DATA/READ/RESTORE.

New modules: interp.c (1445 lines - execution loop and statement
dispatcher), vars.c, arrays.c, input.c. Version bumped to 0.2.0.
16 test programs pass including Leibniz pi and prime sieve.

include/interp.h

@@ -24,9 +24,43 @@ typedef struct {
     /* Default variable types for A-Z (DEFTBL) */
     gw_valtype_t def_type[26];
 
+    /* Variable storage */
+    var_entry_t vars[256];
+    int var_count;
+    array_entry_t arrays[64];
+    int array_count;
+    int option_base;
+
+    /* Control flow stacks */
+    for_entry_t for_stack[16];
+    int for_sp;
+    gosub_entry_t gosub_stack[24];
+    int gosub_sp;
+    while_entry_t while_stack[16];
+    int while_sp;
+
+    /* DEF FN */
+    fn_def_t fn_defs[26];
+
+    /* Run state */
+    program_line_t *cur_line;
+    bool running;
+
+    /* CONT state */
+    uint8_t *cont_text;
+    program_line_t *cont_line;
+
     /* DATA pointer */
     uint8_t *data_ptr;
+    program_line_t *data_line_ptr;
     uint16_t data_line;
+
+    /* Error trapping */
+    uint16_t on_error_line;
+    bool in_error_handler;
+    uint8_t *err_resume_text;
+    program_line_t *err_resume_line;
+    uint16_t err_line_num;
 } interp_state_t;
 
 extern interp_state_t gw;
@@ -35,8 +69,15 @@ extern interp_state_t gw;
 #define LINE_DIRECT 65535
 
 void gw_init(void);
-void gw_exec_line(uint8_t *tokens);
 void gw_exec_direct(const char *line);
+void gw_exec_stmt(void);
+void gw_run_loop(void);
+
+/* Program storage */
+void gw_store_line(uint16_t num, uint8_t *tokens, int len);
+void gw_delete_line(uint16_t num);
+program_line_t *gw_find_line(uint16_t num);
+void gw_free_program(void);
 
 /* CHRGET/CHRGOT - advance/peek the text pointer */
 uint8_t gw_chrget(void);