Split testing into unit and functional tests.

* Split the `test` nimble task into `unittest` and `functest`, with
  corresponding test directories and test runners.
* Added documentation in README regarding building and testing StrawBoss.
* Created a small, simple test project for use in the functional tests.
* Added a `keepEnv` template in the server unit test code to make it easy to
  preserve the working environment for a single unit test to invistigate
  failures manually.

src/test/json/dummy-project.config.json

@@ -1,5 +1,5 @@
 {
-  "name": "test-project-1",
+  "name": "dummy-project",
   "versionCmd": "git describe --all --always",
   "steps": {
     "build": {

src/test/json/strawboss.config.json

@@ -8,12 +8,12 @@
   ],
   "pwdCost": 11,
   "projects": [
-    { "name": "test-project-1",
+    { "name": "dummy-project",
       "repo": "/non-existent/dir",
       "cfgFilePath": "strawhat.json",
       "defaultBranch": "deploy",
       "envVars": { "VAR1": "value" }
     },
-    { "name": "test-strawboss",
-      "repo": "https://git.jdb-labs.com:jdb/test-strawboss.git" } ]
+    { "name": "test-project",
+      "repo": "" } ]
 }