Add Option type & is_some/is_none methods (FuelLabs#31)

* Feat:Add Option type & is_some/is_none methods

* Doc:Improve module-level docs

* Fix:Add generic type T to match

src/lib.sw

@@ -8,6 +8,7 @@ dep chain;
 dep contract_id;
 dep context;
 dep address;
+dep option;
 dep block;
 dep token;
 dep result;

src/option.sw

@@ -0,0 +1,51 @@
+//! Error handling with the `Option` type.
+//!
+//! [`Option<T>`][`Option`] is the type used for representing the existence or absence of a value. It is an enum with the variants, [`Some(T)`], representing
+//! some value, and [`None()`], representing
+//! no value.
+
+library option;
+
+/// `Option` is a type that represents either the existence of a value ([`Some`]) or a value's absence
+/// ([`None`]).
+pub enum Option<T> {
+    /// Contains the value
+    Some: T,
+
+    /// Signifies the absence of a value
+    None: (),
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// Type implementation
+/////////////////////////////////////////////////////////////////////////////
+
+impl Option<T> {
+    /////////////////////////////////////////////////////////////////////////
+    // Querying the contained values
+    /////////////////////////////////////////////////////////////////////////
+
+    /// Returns `true` if the result is [`Some`].
+    fn is_some(self) -> bool {
+        match self {
+            Option::Some(T) => {
+                true
+            },
+            _ => {
+                false
+            },
+        }
+    }
+
+    /// Returns `true` if the result is [`None`].
+    fn is_none(self) -> bool {
+        match self {
+            Option::Some(T) => {
+                false
+            },
+            _ => {
+                true
+            },
+        }
+    }
+}