add unit tests (#60)

also, flatten the workspace into a single crate. I forget what the original reason for the workspace
was -- I think it was added because `cargo t -p testsuite` is nicer than running
`cargo t --test $filename` N times. However, a single crate removes the need to repeat the list of
dependencies in `testsuite/Cargo.toml`

also, document the two sets of tests included with the template and how to run them in the README
file

Cargo.toml

@@ -5,8 +5,13 @@ name = "{{project-name}}"
 edition = "2018"
 version = "0.1.0"
 
-[workspace]
-members = ["testsuite"]
+[lib]
+harness = false
+
+# needed for each integration test
+[[test]]
+name = "integration"
+harness = false
 
 [dependencies]
 cortex-m = "0.7.3"
@@ -17,6 +22,9 @@ panic-probe = { version = "0.3.0", features = ["print-defmt"] }
 # TODO(4) enter your HAL here
 # some-hal = "1.2.3"
 
+[dev-dependencies]
+defmt-test = "0.3.0"
+
 # cargo build/run
 [profile.dev]
 codegen-units = 1