Added missing check for failure on umm_push_heap calls in Esp.cpp (#7767)

Added lost comments for Esp.h

Author: mhightower83

cores/esp8266/Esp.cpp

@@ -984,15 +984,20 @@ void EspClass::enableVM()
 void EspClass::setExternalHeap()
 {
 #ifdef UMM_HEAP_EXTERNAL
-    if (vmEnabled)
-        umm_push_heap(UMM_HEAP_EXTERNAL);
+    if (vmEnabled) {
+        if (!umm_push_heap(UMM_HEAP_EXTERNAL)) {
+            panic();
+        }
+    }
 #endif
 }
 
 void EspClass::setIramHeap()
 {
 #ifdef UMM_HEAP_IRAM
-    umm_push_heap(UMM_HEAP_IRAM);
+    if (!umm_push_heap(UMM_HEAP_IRAM)) {
+        panic();
+    }
 #endif
 }
 

cores/esp8266/Esp.h

@@ -215,10 +215,41 @@ class EspClass {
 #else
         uint32_t getCycleCount();
 #endif // !defined(CORE_MOCK)
+        /**
+         * @brief Installs VM exception handler to support External memory (Experimental)
+         *
+         * @param none
+         * @return none
+         */
         void enableVM();
+        /**
+         * @brief Push current Heap selection and set Heap selection to DRAM.
+         *
+         * @param none
+         * @return none
+         */
         void setDramHeap();
+        /**
+         * @brief Push current Heap selection and set Heap selection to IRAM.
+         *
+         * @param none
+         * @return none
+         */
         void setIramHeap();
+        /**
+         * @brief Push current Heap selection and set Heap selection to External. (Experimental)
+         *
+         * @param none
+         * @return none
+         */
         void setExternalHeap();
+        /**
+         * @brief Restores Heap selection back to value present when
+         * setDramHeap, setIramHeap, or setExternalHeap was called.
+         *
+         * @param none
+         * @return none
+         */
         void resetHeap();
     private:
 #ifdef UMM_HEAP_EXTERNAL