examples: add an example plugin of an eve filetype

examples: add an example plugin of an eve filetype

This is an example of what adding plugin examples to the Suricata repo
could look like.

This plugin is an example plugin for an EVE filetype. It could be
extended to support outputs like Redis, syslog, etc.

There is one issue with adding plugins like this to an autotools
project, the project can't be built with --disable-shared, which is
more of an autotools limitation, and not really a Suricata issue.
Suricata built with --disable-shared will load plugins just fine.

Note that the examples directory was added as DIST_SUBDIRS as we don't
want normal builds to recurse into it and attempt to build the plugin,
its just an example, but we still need to keep distcheck happy.