Move rtic macros to repo root, tune xtask

Cargo.toml

@@ -0,0 +1,28 @@
+[workspace]
+members = [
+    "rtic",
+    "xtask",
+]
+
+[profile.release]
+codegen-units = 1
+lto = true
+
+# do not optimize proc-macro deps or build scripts
+[profile.dev.build-override]
+codegen-units = 16
+debug = false
+debug-assertions = false
+opt-level = 0
+overflow-checks = false
+
+
+[profile.release.build-override]
+codegen-units = 16
+debug = false
+debug-assertions = false
+opt-level = 0
+overflow-checks = false
+
+[patch.crates-io]
+lm3s6965 = { git = "https://github.com/japaric/lm3s6965" }