IOSource reorg.

A bunch of infrastructure work to move IOSource, IOSourceRegistry (now
iosource::Manager) and PktSrc/PktDumper code into iosource/, and over
to a plugin structure.

Other IOSources aren't touched yet, they are still in src/*.

It compiles and does something with a small trace, but that's all I've
tested so far. There are quite certainly a number of problems left, as
well as various TODOs and cleanup; and nothing's cast in stone yet.

Will continue to work on this.
Fixing rebase relicts.
Merge branch 'topic/robin/dynamic-plugins-2.3' into topic/robin/pktsrc
A series of updates and tweaks to the new PktSrc interface.
Prototype of a netmap packet source.

TODO: Add userland BPF filtering so that our filters work.
Converting log writers and input readers to plugins.
Merge branch 'topic/robin/dynamic-plugins-2.3' into topic/robin/reader-writer-plugins
Split the types and attributes reference doc into two docs

Also moved them up in the index so that the more fundamental material
comes before the more advanced material in the table of contents.
Merge remote-tracking branch 'origin/master' into topic/robin/reader-writer-plugins
Final fixes, preparing for merge.
Test case for a dynamic log writer.
Test case for a dynamic input reader.
Merge remote-tracking branch 'origin/master' into topic/robin/reader-writer-plugins
More polishing.
More polishing of some of the branche's changes.
Move DataSeries and ElasticSearch into plugins.
Updating submodule.
Merge remote-tracking branch 'origin/master' into topic/robin/reader-writer-plugins
Merge branch 'topic/robin/reader-writer-plugins' of git.bro.org:bro into topic/robin/reader-writer-plugins

Conflicts:
	scripts/base/frameworks/logging/writers/dataseries.bro
Removing DataSeries and ElasticSearch from configure script.