Support multi-clause patterns as syntactic sugar

And disable multi-patterns clauses. I was originally just controlling
  whether we did disable that from the parser but then I figured we
  could actually support multi-patterns clauses quite easily by simply
  desugaring a multi-pattern into multiple clauses.

  This is only a syntactic sugar, which means that the cost of writing
  that on-chain is as expensive as writing the fully expanded form; yet
  it seems like a useful shorthand; especially for short clause
  expressions.

  This commit however disables multi-pattern when clauses, which we do
  not support in the code-generation. Instead, one pattern on tuples for
  that.

examples/acceptance_tests/078/aiken.lock

@@ -0,0 +1,5 @@
+# This file was generated by Aiken
+# You typically do not need to edit this file
+
+requirements = []
+packages = []

examples/acceptance_tests/078/aiken.toml

@@ -0,0 +1,2 @@
+name = "aiken-lang/acceptance_test_078"
+version = "0.0.0"

examples/acceptance_tests/078/lib/tests.ak

@@ -0,0 +1,45 @@
+type DayOfTheWeek {
+  Monday
+  Tuesday
+  Wednesday
+  Thursday
+  Friday
+  Saturday
+  Sunday
+}
+
+fn is_work(day: DayOfTheWeek) {
+  when day is {
+    Tuesday | Wednesday | Thursday | Friday | Saturday ->
+      True
+    _ ->
+      False
+  }
+}
+
+test is_work_1() {
+  is_work(Thursday)
+}
+
+test is_work_2() {
+  !is_work(Monday)
+}
+
+fn is_happy_hour(day: DayOfTheWeek, current_time: Int) {
+  when day is {
+    Monday | Sunday ->
+      True
+    Tuesday | Wednesday | Thursday | Friday | Saturday if current_time > 18 ->
+      True
+    _ ->
+      False
+  }
+}
+
+test is_happy_hour_1() {
+  is_happy_hour(Sunday, 14)
+}
+
+test is_happy_hour_2() {
+  is_happy_hour(Friday, 22)
+}

examples/acceptance_tests/078/plutus.json

@@ -0,0 +1,8 @@
+{
+  "preamble": {
+    "title": "aiken-lang/acceptance_test_078",
+    "version": "0.0.0",
+    "plutusVersion": "v2"
+  },
+  "validators": []
+}