Refactoring EPS32NVS library to Preferences library (#199)

* Refactoring EPS32NVS library to Preferences library

* Renaming all set* functions to put
* Added functions for float, double and bool

* Small redesign of Preferences API

* added type to put* function names
* for (u)int64_t used functions name with *(U)Long64
* added functions for long and unsigned long (same like int a unsigned int)

libraries/Preferences/examples/StartCounter/StartCounter.ino

@@ -0,0 +1,56 @@
+/*
+ ESP32 start 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
+ storage on ESP32 processor.
+
+ created for arduino-esp32 09 Feb 2017
+ by Martin Sloup (Arcao)
+*/
+
+#include <Preferences.h>
+
+Preferences preferences;
+
+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
+  // RW-mode (second parameter has to be false).
+  // Note: Namespace name is limited to 15 chars
+  preferences.begin("my-app", false);
+
+  // Remove all preferences under 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
+  unsigned int counter = preferences.getUInt("counter", 0);
+
+  // Increase counter
+  counter++;
+
+  // Print counter to a Serial
+  Serial.printf("Current counter value: %u\n", counter);
+
+  // Store counter to the Preferences
+  preferences.putUInt("counter", counter);
+
+  // Close the Preferences
+  preferences.end();
+
+  // Wait 10 seconds
+  Serial.println("Restarting in 10 seconds...");
+  delay(10000);
+
+  // Restart ESP
+  ESP.restart();
+}
+
+void loop() {}