completed

In case of long poll engine requests should be holded until next send
operation from the server starts. To correctly resolve ownership,
shared_ptr should be used on all stages of processing

One can use std::string also for binary data (which may include '\0'). 
Of course, when use such data, one should be avare that str.length() can
be larger then position of first '\0' symbol.

Try to resolve complex ownership problem, when different instances
release reference on THttpCallArg at different time.

To clarify ownership, one uses shared_ptr.
Keep old interfaces, but declare them as deprecated. 

TWebWindow

Provide support of binary interfaces for web socket, long polling and
cefQuery

It is request, which was not recognized by the server.
User can provide alternative processing of such requests.

There is ROOT standard way to decode such data - use it.
Base64 decoding used to send PNG/GPG/SVG images from clients to server.
For the moment there is no other way to transfer binary data from
clients

Use base64 coding for binary data while only text-based sending
supported

Binary data in raw mode provided as ArrayBuffer on the client side.
If one want to use it for reading data as array one should have offset
which is multiple of 4 (for floats) or 8 (for doubles). 
Therefore always adjust offset to be multiple of 8 bytes

In raw mode only response body can be used to transfer information.
Implemented for Qt5 WebEngine, where such limitation should be respected

Should appear as Blob object on client side

One could send now binary messages viw websockets, 
which result as Blob objects on JavaScript side. 
Also combined send of string header and raw buffer will be supported.
For special engines (like longpoll) this will be handled in single
request.

Allows re-use of traditional ROOT diag rewiring by frameworks.

This fixes ROOT-9322

TODO: actually test that we error out

...and have Cache define aliases for its output TDataFrame

We need the side-effects, e.g. declaration of an alias of the
variable's type to the interpreter.

The alias is declared _in the interpreter_, for use by jitted
transformations and actions.

The ID will be used to jit objects in a namespace reserved for this computation graph.