make task.$T.enabled optional

and move the logic that differentiates interrupts from exceptions from the crate
to the procedural macro logic

tests/cfail/critical-section.rs

@@ -21,7 +21,6 @@ app! {
 
     tasks: {
         EXTI0: {
-            enabled: true,
             path: exti0,
             priority: 1,
             resources: [ON],

tests/cfail/duplicated-task.rs

@@ -9,7 +9,6 @@ use rtfm::app;
 
 app! {
     //~^ error proc macro panicked
-    //~| help parsing
     device: stm32f103xx,
 
     tasks: {

tests/cfail/exception.rs

@@ -7,9 +7,7 @@ extern crate stm32f103xx;
 
 use rtfm::app;
 
-app! {
-    //~^ error no associated item named `SYS_TICK` found for type
-    //~| error no associated item named `SYS_TICK` found for type
+app! { //~ error proc macro panicked
     device: stm32f103xx,
 
     tasks: {

tests/cfail/interrupt.rs

@@ -7,14 +7,14 @@ extern crate stm32f103xx;
 
 use rtfm::app;
 
-app! { //~ error no associated item named `EXTI0` found for type
+app! {
+    //~^ error no associated item named `EXTI33` found for type
+    //~| error no associated item named `EXTI33` found for type
     device: stm32f103xx,
 
     tasks: {
-        // ERROR `enabled` needs to be specified for interrupts
-        EXTI0: {
-            priority: 1,
-        },
+        // ERROR this interrupt doesn't exist
+        EXTI33: {},
     },
 }
 

tests/cfail/lock.rs

@@ -18,21 +18,18 @@ app! {
 
     tasks: {
         EXTI0: {
-            enabled: true,
             path: exti0,
             priority: 1,
             resources: [MAX, ON],
         },
 
         EXTI1: {
-            enabled: true,
             path: exti1,
             priority: 2,
             resources: [ON],
         },
 
         EXTI2: {
-            enabled: true,
             path: exti2,
             priority: 16,
             resources: [MAX],

tests/cfail/token-outlive.rs

@@ -17,14 +17,12 @@ app! {
 
     tasks: {
         EXTI0: {
-            enabled: true,
             path: exti0,
             priority: 1,
             resources: [STATE],
         },
 
         EXTI1: {
-            enabled: true,
             path: exti1,
             priority: 2,
             resources: [STATE],

tests/cfail/token-transfer.rs

@@ -17,7 +17,6 @@ app! { //~ error bound `rtfm::Threshold: core::marker::Send` is not satisfied
 
     tasks: {
         EXTI0: {
-            enabled: true,
             path: exti0,
             priority: 1,
             resources: [TOKEN],

tests/cfail/wrong-threshold.rs

@@ -18,14 +18,12 @@ app! {
 
     tasks: {
         EXTI0: {
-            enabled: true,
             path: exti0,
             priority: 1,
             resources: [A, B],
         },
 
         EXTI1: {
-            enabled: true,
             path: exti1,
             priority: 2,
             resources: [A, B],