feat(cli): --version, a CHANGELOG, and a release target

Groundwork for tagging. The project had no version anywhere: not in
dune-project, not in the binary, no CHANGELOG, no tags.

The version lives in two places -- dune-project, which generates
colitur.opam, and a constant in bin/main.ml, which is what --version
prints. Two rather than one because dune's watermarking only substitutes
in a release tarball, so a binary built the ordinary way from a checkout
would report a placeholder. The release target rewrites both and then
re-checks both, and finally requires the freshly built binary to report
the version it just wrote: a release that bumped one and not the other
would ship a binary disagreeing with its own package metadata.

--version is deliberately not embedded in the help text. cli.t pins
help's first line, and a version there would mean editing a test
expectation every release for no gain.

The release target mirrors lectio's, refusals included: no release from a
dirty tree, none without a CHANGELOG entry for that version, none whose
version bump silently failed to apply, and `make check` -- the full
1583-9999 sweep, not the sampling suite -- must pass before the tag is
created.

1 files changed, 15 insertions, 0 deletions

diff --git a/bin/main.ml b/bin/main.ml
index 573f190..141f016 100644
--- a/bin/main.ml
+++ b/bin/main.ml
@@ -336,6 +336,17 @@ let readings_report y = resolved_year_report ~line:readings_line y
    pager or grepped); being invoked wrongly is an error, so [usage] prints a
    one-liner to stderr and exits 2, keeping stdout clean for whatever the
    caller was really trying to capture. *)
+(* Kept in lockstep with dune-project's own [(version ...)] by `make release`,
+   which bumps BOTH and refuses to proceed if either edit did not take. Two
+   places rather than one because dune's watermarking (`dune subst`) only
+   substitutes in a release tarball, not in a plain `dune build` from a
+   checkout, so a binary built the ordinary way would report a placeholder.
+   A constant edited by the release target is what lectio does too, for the
+   same reason. Deliberately NOT embedded in [help_text]: the cram test pins
+   help's first line, and a version in it would make every release edit a
+   test expectation for no gain. *)
+let version = "0.1.0"
+
 let help_text =
   {|colitur -- deterministic liturgical calendar engine (Roman rite, 1962)
 
@@ -345,6 +356,7 @@ usage:
   colitur day <year>         the resolved day identity, one line per day
   colitur readings <year>    the Mass reading citations, one line per day
   colitur -h, --help         this help
+  colitur -V, --version      print the version and exit
 
 <year> is a civil year, 1583..9999 inclusive. Each report covers 1 January to
 31 December of that year, not a liturgical year.
@@ -394,6 +406,9 @@ let with_year ys f =
 let () =
   match Sys.argv with
   | [| _; ("-h" | "--help" | "help") |] -> print_help ()
+  | [| _; ("-V" | "--version" | "version") |] ->
+      print_endline version;
+      exit 0
   | [| _; "easter"; ys |] -> with_year ys easter_report
   | [| _; "temporal"; ys |] -> with_year ys temporal_report
   | [| _; "day"; ys |] -> with_year ys day_report