minor build improvements

Sending of partial packets

- ALIAS CMake target fishnets::fishnets

- Latest CPM and dependencies
- Compact copyright notice in sources

- Use modern asio executors (as opposed to the compatibility ones)

- Prevent asio exceptions when socket disconnects while we're trying to get endpoint info
- Test fixes

- Session heartbeats

- No pure virtual funcs in session

Help with factory func fwd declaration

- switch to itlib::span

- latest deps

* Revamped client. Multiple connections. Support reconnect flow

* Request target queries
* Fix for tasks which outlive sessions
* Latest deos

- Customization of certain options for new sessions

- WebSocketEndpointInfo as argument for server session factory
- Allow server sesion factory to return nullptr (server deny)
- Moved WebSocketEndpointInfo to a separate header
- CMake option to disable SSL and SecureWebSockets
- New example: Terminal Client

- Getting of endpoint info from session

- Fixed dev builds' boost-cmake (latest download link)