Add HTTPClient, ported from the ESP8266 (#784)

Remove the need to have a separate WiFiClient that's destroyed after
the HTTPClient.  Let the object handle its own client, and pass through
any SSL requests.

Also supports the original ::begin methods which need a
WiFiClient(Secure) to be passed in and managed by the app.

libraries/HTTPClient/examples/BasicHttpClient/BasicHttpClient.ino

@@ -0,0 +1,75 @@
+/**
+   BasicHTTPClient.ino
+
+   Created on: 24.05.2015
+
+*/
+
+#include <Arduino.h>
+#include <WiFi.h>
+#include <HTTPClient.h>
+
+#ifndef STASSID
+#define STASSID "your-ssid"
+#define STAPSK "your-password"
+#endif
+
+const char *ssid = STASSID;
+const char *pass = STAPSK;
+
+WiFiMulti WiFiMulti;
+
+void setup() {
+
+  Serial.begin(115200);
+  // Serial.setDebugOutput(true);
+
+  Serial.println();
+  Serial.println();
+  Serial.println();
+
+  for (uint8_t t = 4; t > 0; t--) {
+    Serial.printf("[SETUP] WAIT %d...\n", t);
+    Serial.flush();
+    delay(1000);
+  }
+
+  WiFiMulti.addAP(ssid, pass);
+}
+
+void loop() {
+  // wait for WiFi connection
+  if ((WiFiMulti.run() == WL_CONNECTED)) {
+
+    HTTPClient http;
+
+    Serial.print("[HTTP] begin...\n");
+    if (http.begin("http://httpbin.org")) {  // HTTP
+
+
+      Serial.print("[HTTP] GET...\n");
+      // start connection and send HTTP header
+      int httpCode = http.GET();
+
+      // httpCode will be negative on error
+      if (httpCode > 0) {
+        // HTTP header has been send and Server response header has been handled
+        Serial.printf("[HTTP] GET... code: %d\n", httpCode);
+
+        // file found at server
+        if (httpCode == HTTP_CODE_OK || httpCode == HTTP_CODE_MOVED_PERMANENTLY) {
+          String payload = http.getString();
+          Serial.println(payload);
+        }
+      } else {
+        Serial.printf("[HTTP] GET... failed, error: %s\n", http.errorToString(httpCode).c_str());
+      }
+
+      http.end();
+    } else {
+      Serial.printf("[HTTP} Unable to connect\n");
+    }
+  }
+
+  delay(10000);
+}