Add EEPROMClass and examples (#1034)

* enchanced EEPROMClass

* Added eeprom examles and modified partition

* added eeprom class and extra examples

* No changes

* No changes

* added eeprom class and examples

* fixed typo

* length() returns user-defined sector size

* updated and annotated example

libraries/EEPROM/examples/eeprom_class/eeprom_class.ino

@@ -0,0 +1,92 @@
+/*
+  ESP32 eeprom_class example with EEPROM library
+
+  This simple example demonstrates using EEPROM library to store different data in
+  ESP32 Flash memory in a multiple user-defined EEPROM partition (0x1000 or 4KB max size or less).
+  
+  Install 'ESP32 Partiton Manager' ONCE from https://github.com/francis94c/ESP32Partitions
+  And generate different partitions with 'partition_name'
+  Usage: EEPROMClass ANY_OBJECT_NAME("partition_name", size);
+  
+  Generated partition that would work perfectly with this example
+  #Name,   Type, SubType, Offset,   Size,    Flags
+  nvs,     data, nvs,     0x9000,   0x5000,
+  otadata, data, ota,     0xe000,   0x2000,
+  app0,    app,  ota_0,   0x10000,  0x140000,
+  app1,    app,  ota_1,   0x150000, 0x140000,
+  eeprom0, data, 0x99,    0x290000, 0x1000,
+  eeprom1, data, 0x9a,    0x291000, 0x500,
+  eeprom2, data, 0x9b,    0x292000, 0x100,
+  spiffs,  data, spiffs,  0x293000, 0x16d000,
+
+  Created for arduino-esp32 on 25 Dec, 2017
+  by Elochukwu Ifediora (fedy0)
+*/
+
+#include "EEPROM.h"
+
+// Instantiate eeprom objects with parameter/argument names and size same as in the partition table
+EEPROMClass  NAMES("eeprom0", 0x1000);
+EEPROMClass  HEIGHT("eeprom1", 0x500);
+EEPROMClass  AGE("eeprom2", 0x100);
+
+void setup() {
+  // put your setup code here, to run once:
+  Serial.begin(115200);
+  Serial.println("Testing EEPROMClass\n");
+  if (!NAMES.begin(NAMES.length())) {
+    Serial.println("Failed to initialise NAMES");
+    Serial.println("Restarting...");
+    delay(1000);
+    ESP.restart();
+  }
+  if (!HEIGHT.begin(HEIGHT.length())) {
+    Serial.println("Failed to initialise HEIGHT");
+    Serial.println("Restarting...");
+    delay(1000);
+    ESP.restart();
+  }
+  if (!AGE.begin(AGE.length())) {
+    Serial.println("Failed to initialise AGE");
+    Serial.println("Restarting...");
+    delay(1000);
+    ESP.restart();
+  }
+
+  char* name = "Teo Swee Ann";
+  double height = 5.8;
+  uint32_t age = 47;
+
+  // Write: Variables ---> EEPROM partitions
+  NAMES.put(0, name);
+  HEIGHT.put(0, height);
+  AGE.put(0, age);
+  Serial.print("name: ");   Serial.println(name);
+  Serial.print("height: "); Serial.println(height);
+  Serial.print("age: ");    Serial.println(age);
+  Serial.println("------------------------------------\n");
+
+  // Clear variables
+  name = '\0';
+  height = 0;
+  age = 0;
+  Serial.print("name: ");   Serial.println(name);
+  Serial.print("height: "); Serial.println(height);
+  Serial.print("age: ");    Serial.println(age);
+  Serial.println("------------------------------------\n");
+
+  // Read: Variables <--- EEPROM partitions
+  NAMES.get(0, name);
+  HEIGHT.get(0, height);
+  AGE.get(0, age);
+  Serial.print("name: ");   Serial.println(name);
+  Serial.print("height: "); Serial.println(height);
+  Serial.print("age: ");    Serial.println(age);
+  
+  Serial.println("Done!");
+}
+
+void loop() {
+  // put your main code here, to run repeatedly:
+
+}