Add GitHub Actions CI with automated build and test. Implement real
terminal I/O with raw mode (enable_raw/disable_raw, proper INKEY$
polling via VMIN=0/VTIME=0, INPUT$ function). Add Sixel graphics
engine with virtual framebuffer (SCREEN 1: 320x200, SCREEN 2:
640x200), Bresenham line drawing, midpoint circle, flood fill PAINT,
DRAW mini-language parser, and Sixel encoder with RLE. Replace all
graphics stubs with real implementations (PSET, LINE, CIRCLE, DRAW,
PAINT, COLOR, SCREEN, POINT). Fix AND/OR/XOR operator precedence
to be lower than relational operators. Add 13 classic test programs
(39 total). Bump version to 0.5.0.
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.
Eremey Valetov