decoder_raw: Add option output_format

This option can use the following values:
- 'textual', to adjust output format to textual
- 'binary', to adjust format to binary
Default is textual as remains as such if nothing is specified.

Note that output format impacts only the get/peek SQL functions able to
query a replication slot.
decoder_raw: Fix regression tests

Regression tests have been broken by two things:
- Modification of option name from include-transaction to
include_transaction only applied on code and node regressions
- pg_create_logical_replication_slot returns slot_name and not anymore
slotname as column name.
Add central Makefile for all plugins

Useful to install, clean or test everything at the same time.
Rewrite README

For details about this project and better format.
Update Copyright headers and file headers

All the files of this project have now top-comment blocks more uniform.
Copyright dates and names have been updated as well.
Correct incorrect header format
jsonlog: Implementation of module generating logs in JSON format

The basics are here and in place, taking necessary routines from elog.c.
More fields and a better tracking of useless things taht should not be
tracked will be added soon.
jsonlog: Add same level of messages as csvlog

The field output selection is made more severe as well: are printed only
field values that are necessary to reduce log volume.
Mention in README modules manipulating log format of server
jsonlog: Add this module in global Makefile as a subdirectory

This has been forgotten in previous commits.
jsonlog: Simplify write_pipe_chunks as everything is stderr
receiver_raw: improve feedback handling to server

The applied position is updated as well when sending feedback, and the
default value of connection string to connect to remote is updated to
include application_name, something useful for tracking replication
in pg_stat_replication on a master for example.
receiver_raw: Add receiver.sync_mode to enforce WAL feedback

This is helpful when using synchronous mode on master with this logical
receiver.
decoder_raw: Realign a couple of routine definitions
decoder_raw: Rename TestDecodingData to DecoderRawData

This is more consistent with the plugin naming.