Created ydb_branch_file_input module.

Equivalent to currently existing ydb_file_input module in most regards.
However, no longer has any use for the schema, as it will be stored in
the branch node instead. This means that the plan node will simply
passes the raw tuple data (i.e. non-#ydb_tuple{}s) to the branch node.
Created ydb_branch_socket_input module.

Equivalent to currently existing ydb_socket_input module in most
regards. However, no longer has any use for the schema, as it will be
stored in the branch node isntead.  This means that the plan node
simply passes the raw tuple data (i.e. non-#ydb_tuple{}s) tothe branch
node.
Changed message branch {file,socket} input modules send.

Wrapped tuple in {'$gen_cast', ...} tuple so that branch node receives
message through handle_cast/2, rather than handle_info/2.
Added support for branch node to receive tuples.

Converts the raw-form tuples into ydb_tuple()s by using the
ydb_input_node_utils:make_tuple/3, which are then sent to the
appropriate listeners.
Added support for retrieving the pid of the branch node.

Works only if the application has been started.
Created planner function to work with branch nodes.

Implementation is nearly identical to make_no_branch/1, but allows
listeners to be of the form
    {InputStream :: atom(), BranchType :: atom()}
rather than simply the registerd name of the input stream.
Added support for registering self as listener to branch node.

Uses the pid of the branch and the type to subscribe to, and simply
calls to ydb_branch_node:add_listener/3.
Fixed issue with using dict:fetch/2.

If no listeners of a type existed, then would generate exception. Now
use dict:find/2 and create a new set upon the return value of 'error'.
Added support for calling relegate/{2,3} on pids.

Necessary in order to start the read process of the file input node.
Fixed a couple issues in ydb_branch_node module.

Made the same mistake as in ydb_plan_node, where the list of
subscribers is actually composed of pairs {pid(), ref()}.

Had invalid return value of {ok, State} rather {noreply, State} when
received tuples from an input stream.
Change ydb_query module to use ydb_planner/make_nonjoin/1.
Merge branch 'branch_planner'