Finished(?) decompression stuff

src/decomp/c/lz4.zig

@@ -0,0 +1,12 @@
+const std = @import("std");
+
+const c = @import("../../c_libs.zig").c;
+const Decompressor = @import("../../decomp.zig");
+
+interface: Decompressor = .{ .vtable = .{ .stateless = stateless } },
+
+pub fn stateless(_: std.mem.Allocator, in: []u8, out: []u8) Decompressor.Error!usize {
+    const res = c.LZ4_decompress_safe(in.ptr, out.ptr, in.len, out.len);
+    if (res > 0) return @abs(res);
+    return Decompressor.Error.ReadFailed; // TOOD: Find out what errors can be returned.
+}