Document blurhash

Add documentation from the blurhash reference implementation to the code.

src/blurhash.h

@@ -5,6 +5,24 @@
 
 #include <stdint.h>
 
+/**
+ * @brief Returns the pixel array of the result image given the blurhash string.
+ *
+ * @param blurhash a string representing the blurhash to be decoded.
+ * @param width the width of the resulting image.
+ * @param height the height of the resulting image.
+ * @param punch the factor to improve the contrast, default = 1.
+ * @param nChannels the number of channels in the resulting image array, 3 = RGB, 4 = RGBA.
+ *
+ * @return A pointer to memory region where pixels are stored in (H, W, C) format.
+ */
 uint8_t *decode(const char *blurhash, int width, int height, int punch, int nChannels);
 
+/**
+ * @brief Checks if the Blurhash is valid or not.
+ *
+ * @param blurhash a string representing the blurhash.
+ *
+ * @return A bool (true if it is a valid blurhash, else false).
+ */
 bool isValidBlurhash(const char *blurhash);