Deprecate beast::flat_stream and beast::ssl_stream

[ashtum]

Closes #1995

[cppalliance-bot]

An automated preview of the documentation is available at https://2875.beastdocs.prtest.cppalliance.org/libs/beast/doc/html/index.html

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.21%. Comparing base (cf72589) to head (a0d2fe4).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2875      +/-   ##
===========================================
+ Coverage    93.05%   93.21%   +0.16%     
===========================================
  Files          178      177       -1     
  Lines        13694    13670      -24     
===========================================
  Hits         12743    12743              
+ Misses         951      927      -24     

see 1 file with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update cf72589...a0d2fe4. Read the comment docs.

[vinniefalco]

Commit messages should start with nouns:

std::bind is superfluous in some examples ssl_stream does not use flat_stream net::ssl::stream is canonical in examples net::ssl::stream is canonical in snippets ssl_stream and flat_stream are deprecated

[cppalliance-bot]

An automated preview of the documentation is available at https://2875.beastdocs.prtest.cppalliance.org/libs/beast/doc/html/index.html

[cppalliance-bot]

An automated preview of the documentation is available at https://2875.beastdocs.prtest.cppalliance.org/libs/beast/doc/html/index.html