Replace godot-gifexporter with godot-gdgifexporter (#295)

Add exporting in a separate thread and a progress bar
Remove background color option from gif export

addons/gdgifexporter/gif-lzw/lsbbitunpacker.gd

@@ -0,0 +1,41 @@
+extends Node
+
+
+class LSB_LZWBitUnpacker:
+	var chunk_stream: PoolByteArray
+	var bit_index: int = 0
+	var byte: int
+	var byte_index: int = 0
+
+	func _init(_chunk_stream: PoolByteArray):
+		chunk_stream = _chunk_stream
+		self.get_byte()
+
+	func get_bit(value: int, index: int) -> int:
+		return (value >> index) & 1
+
+	func set_bit(value: int, index: int) -> int:
+		return value | (1 << index)
+
+	func get_byte():
+		byte = chunk_stream[byte_index]
+		byte_index += 1
+		bit_index = 0
+
+	func read_bits(bits_count: int) -> int:
+		var result: int = 0
+		var result_bit_index: int = 0
+
+		for _i in range(bits_count):
+			if self.get_bit(byte, bit_index) == 1:
+				result = self.set_bit(result, result_bit_index)
+			result_bit_index += 1
+			bit_index += 1
+
+			if bit_index == 8:
+				self.get_byte()
+
+		return result
+
+	func remove_bits(bits_count: int) -> void:
+		self.read_bits(bits_count)