Refactored sniffer class to take a SnifferConfigurator to do the setup.

This way it is easier to extend the different configuration capabilities.
Created gitignore file to exclude build directory and config.h automatically generated file.
Changed the name to SnifferConfiguration, it sounds better.
Updated the examples to work with the new Sniffer constructor using the SnifferConfiguration object.
Added back the original constructors of the Sniffer and FileSniffer to keep compatibility. Tagged them as deprecated, though.

Changed the default if_mask to 0 as PCAP_NETMASK_UNKNOWN is still not present in all versions of pcap.

Snap length is always set and it's default value is of 65535 not 0.
Added documentation for SnifferConfiguration.
Fixed using pcap_compile on a not-yet activated pcap handle.
The timeout Sniffer option is set to 1000 by default.
Merge pull request #33 from mfontanini/sniffer-config-object

Sniffer config object