Fixed GCC warning caused by MQTTClient_connectOptions_initializer constant missing a value for the 'returned' sub-structure of MQTTClient_connectOptions structure.

GCC check throwing the warning: 'missing-field-initializers', enabled by option -Wextra
GCC version 4.7.2

Error message:
warning: missing initializer for field 'returned' of 'MQTTClient_connectOptions' [-Wmissing-field-initializers]
MQTTClient_connectOptions client_opt = MQTTClient_connectOptions_initializer;
^
Signed-off-by: Sylvain Miermont <s.miermont@idosens.com>

Signed-off-by: Ryan Pendleton <me@ryanp.me>

Bug: 486548

Bug: 472250

Bug: 479376

Bug: 480363

Automatic reconnect and offline buffering

Conflicts:
	src/Socket.c

Bug: 484496

Build cmake fix

Fix samples

According to ISO/IEC 9899:2011, section 7.22.4.4 (The exit function),
"the constant EXIT_FAILURE is the implementation independent way to
issue failures to exit(3)." Whereas EXIT_SUCCESS is the standard way
to return success. Favor this platform independent constants than the
literal numbers.
Signed-off-by: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>

According to ISO/IEC 9899:2011, section 6.7.6.3, "Function declarators
(including prototypes)": "The special case of an unnamed parameter of
type void as the only item in the list specifies that the function has
no parameters."
Signed-off-by: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>

Reduce the chance of the default value printed being different from
the actual default value used.
Signed-off-by: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>

Add the newline (\n) at the end of --maxdatalen option. Thus, the
usage menu is shown with all options at their own lines.

Also add the command's parameter and its default value on usage
menu.
Signed-off-by: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>

Add a common pattern for the default Client ID of the example applications.
Signed-off-by: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>

This option provides a configurable Keep Alive interval. This
configuration allows a better analysis of PINGREQ and PINGRESP
packages on tools like Wireshark.
Signed-off-by: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>