add main engine library + minimal glfw linking example

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

src/main.zig

@@ -0,0 +1,8 @@
+const std = @import("std");
+const testing = std.testing;
+
+const glfw = @import("glfw");
+
+test "glfw_basic" {
+    glfw.basicTest();
+}