Pattern guards for functions and switch statements (#339)

* Add case guards to parser

* Add pattern guards to infer types and fcode generation

* Add functions guards

* Add test for patterns guards

* Update docs

* Update CHANGELOG.md

* Remove stateful context from Env for guards

* Elaborate on guards

* Add failing test for stateful pattern guards

* Implement multiple guards

* Fix tests

* Disable aevm related tests

* Split the sentence before if and otherwise

* Fix type in docs

* Implement multiple exprs in the same guard

* Fix pretty printing

* Change tests to include multiple guards

* Add test for non-boolean guards

* Desugar clauses with guards

* Fix incomplete patterns bug

* Fix docs

* Compile to icode when no guards are used

* Revert "Disable aevm related tests"

This reverts commit e828099bd97dffe11438f2e48f3a92ce3641e85b.

test/contracts/non_boolean_pattern_guard.aes

@@ -0,0 +1,4 @@
+contract C =
+  type state = int
+
+  entrypoint init(x) | "y" = 1

test/contracts/patterns_guards.aes

@@ -0,0 +1,19 @@
+include "List.aes"
+
+contract C =
+  type state = int
+
+  entrypoint init() = f([1, 2, 3, 4])
+
+  function
+    f(x::[])
+      | x > 1, x < 10 = 1
+      | x < 1 = 9
+    f(x::y::[]) = 2
+    f(x::y::z) = switch(z)
+      [] => 4
+      a::[]
+        | a > 10, a < 20 => 5
+        | a > 5 => 8
+      b | List.length(b) > 5 => 6
+      c => 7

test/contracts/stateful_pattern_guard.aes

@@ -0,0 +1,10 @@
+contract C =
+  type state = int
+
+  entrypoint init() = f(4)
+
+  function
+    f(x) | x > 0 = 1
+    f(x) | g(x) = 2
+
+  stateful function g(x) = x < 0