Styled text with message entities

Telegram supports styled text using message entities.

A client that wants to send styled messages would simply have to integrate a Markdown/HTML parser, and generate an array of message entities by iterating through the parsed tags.

Special care must be taken to consider the UTF-8 length of strings when generating message entities, see example implementations: tdlib, MadelineProto.

Nested entities are supported, for example the following HTML/Markdown aliases for message entities can be used:

```c++
code
```