Small grammar fixes and clarifications (#1003)

* Small grammar fixes and clarifications

Just fixed some small grammar issues in the comments and clarified a few things that might seem confusing.

* More spelling fixes that I introduced...

libraries/Preferences/examples/StartCounter/StartCounter.ino

 /*
- ESP32 start counter example with Preferences library
+ ESP32 startup counter example with Preferences library.
 
- This simple example demonstrate using Preferences library to store how many times
- was ESP32 module started. Preferences library is wrapper around Non-volatile
+ This simple example demonstrates using the Preferences library to store how many times
+ the ESP32 module has booted. The Preferences library is a wrapper around the Non-volatile
  storage on ESP32 processor.
 
  created for arduino-esp32 09 Feb 2017
@@ -17,29 +17,29 @@ void setup() {
   Serial.begin(115200);
   Serial.println();
 
-  // Open Preferences with my-app namespace. Each application module, library, etc.
-  // has to use namespace name to prevent key name collisions. We will open storage in
+  // Open Preferences with my-app namespace. Each application module, library, etc
+  // has to use a namespace name to prevent key name collisions. We will open storage in
   // RW-mode (second parameter has to be false).
-  // Note: Namespace name is limited to 15 chars
+  // Note: Namespace name is limited to 15 chars.
   preferences.begin("my-app", false);
 
-  // Remove all preferences under opened namespace
+  // Remove all preferences under the opened namespace
   //preferences.clear();
 
   // Or remove the counter key only
   //preferences.remove("counter");
 
-  // Get a counter value, if key is not exist return default value 0
-  // Note: Key name is limited to 15 chars too
+  // Get the counter value, if the key does not exist, return a default value of 0
+  // Note: Key name is limited to 15 chars.
   unsigned int counter = preferences.getUInt("counter", 0);
 
-  // Increase counter
+  // Increase counter by 1
   counter++;
 
-  // Print counter to a Serial
+  // Print the counter to Serial Monitor
   Serial.printf("Current counter value: %u\n", counter);
 
-  // Store counter to the Preferences
+  // Store the counter to the Preferences
   preferences.putUInt("counter", counter);
 
   // Close the Preferences
@@ -53,4 +53,4 @@ void setup() {
   ESP.restart();
 }
 
-void loop() {}
\ No newline at end of file
+void loop() {}