check version bump on library modifications (#127)

tox.ini

@@ -75,8 +75,13 @@ deps =
 commands =
     charm: mypy {[vars]src_path} {posargs}
     lib: mypy --python-version 3.5 {[vars]lib_path} {posargs}
+    lib: /usr/bin/env sh -c 'for m in $(git diff main --name-only {[vars]lib_path}); do \
+    lib:    if ! git diff $m | grep -q "+LIBPATCH\|+LIBAPI"; then \
+    lib:        echo "You forgot to bump the version on $m!"; exit 1; \
+    lib:    fi; done'
     unit: mypy {[vars]tst_path}/unit {posargs}
     integration: mypy {[vars]tst_path}/integration {posargs}
+allowlist_externals = /usr/bin/env
 
 [testenv:reqs]
 description = Check for missing or unused requirements