Fix nREPL on Windows; add a version string

The nREPL server bound its loopback socket through libc process symbols,
which don't carry the socket entry points on Windows — they live in
ws2_32.dll and aren't in joltc.exe's export table, so --nrepl-server died
with "no entry for socket". Load ws2_32 before the foreign bindings there,
call WSAStartup once, and use Winsock's closesocket and int-typed
recv/send. Also fix SOL_SOCKET/SO_REUSEADDR, which the old macos-only
check got wrong on Windows.

Bake a version string into the self-contained binary at build time (from
$JOLT_VERSION, else git describe) and expose it via jolt.host/jolt-version:
--version / -V print it, and it shows in --help, the repl banner, and the
nREPL startup line. Dev runs off bin/joltc read it from git describe.

Add -e to the help output.

host/chez/loader.ss

@@ -384,3 +384,14 @@
 (def-var! "jolt.host" "load-namespace" (lambda (n) (load-namespace n) jolt-nil))
 (def-var! "jolt.host" "file-exists?" (lambda (p) (if (file-exists? p) #t #f)))
 (def-var! "jolt.host" "getenv" (lambda (n) (let ((v (getenv n))) (if v v jolt-nil))))
+
+;; jolt version string. A self-contained binary build bakes the real tag into the
+;; saved heap by emitting (set! jolt-baked-version "…") in flat.ss; a dev run off
+;; the seed leaves it #f and falls back to $JOLT_VERSION (bin/joltc sets it from
+;; `git describe`), then "dev".
+(define jolt-baked-version #f)
+(def-var! "jolt.host" "jolt-version"
+  (lambda ()
+    (or jolt-baked-version
+        (let ((v (getenv "JOLT_VERSION"))) (and v (> (string-length v) 0) v))
+        "dev")))