cli: babashka-style flags (--version, --eval, --main, nrepl-server)

Add --version/version, -e/--eval, -f/--file, -m/--main (require NS and apply
its -main to *command-line-args*), and nrepl-server/--nrepl-server taking an
optional [host:]port (nrepl stays an alias). repl/help/-h round it out.

Also rewrite doc/tools-deps.md as design notes for the now-implemented deps
support (it still read as pre-implementation research), and note the new flags
in the README. Test: cli-test runs the flags from source.

test/integration/cli-test.janet

@@ -0,0 +1,36 @@
+# Smoke-test the command-line flags by running main.janet from source (no build
+# needed, so it can't go stale).
+
+(defn- run [& args]
+  (def p (os/spawn ["janet" "src/jolt/main.janet" ;args] :p {:out :pipe :err :pipe}))
+  (def out (:read (p :out) :all))
+  (os/proc-wait p)
+  (string (or out "")))
+
+(var fails 0)
+(defn check [label got pred]
+  (if (pred got) (print "  ok   " label)
+    (do (++ fails) (printf "  FAIL %s: got %q" label got))))
+
+(defn- has [sub] (fn [s] (string/find sub s)))
+
+(check "--version"  (run "--version")            (has "jolt v"))
+(check "version"    (run "version")              (has "jolt v"))
+(check "--help"     (run "--help")               (has "Usage"))
+(check "help lists nrepl-server" (run "help")    (has "nrepl-server"))
+(check "-e"         (run "-e" "(+ 1 2)")         (has "3"))
+(check "--eval"     (run "--eval" "(* 6 7)")     (has "42"))
+
+# -m requires a namespace and calls its -main with the remaining args
+(def tmp (string (or (os/getenv "TMPDIR") "/tmp") "/jolt-cli-" (os/time)))
+(os/mkdir tmp) (os/mkdir (string tmp "/app"))
+(spit (string tmp "/app/core.clj")
+      "(ns app.core)\n(defn -main [& args] (println \"MAIN\" (count args)))\n")
+(os/setenv "JOLT_PATH" tmp)
+(check "-m calls -main with args" (run "-m" "app.core" "a" "b") (has "MAIN 2"))
+(os/setenv "JOLT_PATH" nil)
+(os/rm (string tmp "/app/core.clj")) (os/rmdir (string tmp "/app")) (os/rmdir tmp)
+
+(if (> fails 0)
+  (error (string "cli-test: " fails " failing check(s)"))
+  (print "\nAll CLI tests passed!"))