Bump to 0.1.1: fix bugs, rewrite tests

Bug fixes:
- Fix Zeller's formula for Julian calendar (separate branch without
  century correction) and use rem_euclid for negative modulo safety
- Pass country code (cc=) to isdayoff.ru API in holiday plugin
- Sync clap --version with Cargo.toml (was hardcoded "1.0.0")

Tests:
- Rename integration_tests.rs to unit_tests.rs (they are unit tests)
- Fix race condition on env vars in plugin tests (Mutex + remove_var)
- Fix incorrect assertions (color tty detection, locale fallback)
- Add missing test cases: Julian/Gregorian Zeller, display date
  parsing, Sunday offset, week numbers, edge cases (87 tests total)
- Remove brittle version-checking tests

Cargo.lock

@@ -134,7 +134,7 @@ checksum = "1e748733b7cbc798e1434b6ac524f0c1ff2ab456fe201501e6497c8417a4fc33"
 
 [[package]]
 name = "cal"
-version = "0.1.0"
+version = "0.1.1"
 dependencies = [
  "assert_cmd",
  "chrono",
@@ -319,7 +319,7 @@ checksum = "2304e00983f87ffb38b55b444b5e3b60a884b5d30c0fca7d82fe33449bbe55ea"
 
 [[package]]
 name = "holiday_highlighter"
-version = "0.1.0"
+version = "0.1.1"
 dependencies = [
  "chrono",
  "libc",