Move source code to src directory

src/index.zig

@@ -0,0 +1,8 @@
+pub const uapi = @import("uapi.zig");
+
+pub const getChip = @import("gpio.zig").getChip;
+pub const getChipZ = @import("gpio.zig").getChipZ;
+pub const getChipByFd = @import("gpio.zig").getChipByFd;
+pub const Chip = @import("gpio.zig").Chip;
+pub const Lines = @import("gpio.zig").Lines;
+pub const Line = @import("gpio.zig").Line;