Set up PlatformIO project for EL512.256-H on ESP32

PlatformIO skeleton (esp32dev, Arduino, Adafruit GFX) with a local EL512
library: EL512Panel (1 bpp framebuffer, two-bit-mode row encoder, I2S DMA
refresh stub) and EL512_GFX (Adafruit_GFX subclass). Adds a test sketch,
pin map, README with wiring and timing, and moves the datasheet to
docs/datasheet/.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

include/pins.h

@@ -0,0 +1,22 @@
+// Pin map for the EL512.256-H panel on an ESP-WROOM-32 (esp32dev).
+//
+// VCLK, VID, TVID, HS and VS are driven by I2S0 in 8-bit parallel (LCD) mode,
+// so their levels come from a DMA byte stream. ENABLE and _LOWPWR are plain GPIO.
+#pragma once
+
+#include <stdint.h>
+
+namespace el512pins {
+
+// I2S-driven signals
+constexpr int8_t VCLK = 18;  // I2S0 WS/clock out -> panel VCLK
+constexpr int8_t VID  = 19;  // byte bit 0
+constexpr int8_t TVID = 21;  // byte bit 1
+constexpr int8_t HS   = 22;  // byte bit 2
+constexpr int8_t VS   = 23;  // byte bit 3
+
+// Static control lines
+constexpr int8_t ENABLE  = 25;  // high = display enabled
+constexpr int8_t LOWPWR_N = 26; // _LOWPWR, active low
+
+}  // namespace el512pins