Various updates

[sandeepmistry]

Including:

• Renaming library name to ArduinoHttpClient and update library metadata accordingly
• Changing server host/IP and port to be constructor arguments
• New API's for reading response headers (headerAvailable(), readHeaderName(), readHeaderValue())
• Support for connection keep-alive via new connectionKeepAlive() API
• Support to disable default request headers using new noDefaultRequestHeaders() API
• Make calling skipResponseHeaders() optional, if responseStatusCode() is called
• Change example to use WiFi101 (instead of Ethernet)
• Removed support for setting custom user agent (easy to add back if we need it)
• Remove disabled proxy mode support
• Corrected some warnings