…erly handle CHTSH environment variable, which override default CHTSH_HOME path

This should fix current build failure with timeout
https://travis-ci.org/github/chubin/cheat.sh/builds/741308362#L402

`--connect-timeout` didn't work, because Docker allows it, but breaks,
because nothing is listening on the other side, giving this error.

    $ curl --connect-timeout 10 http://localhost:8002
    curl: (56) Recv failure: Connection reset by peer
    The command "curl --connect-timeout 10 http://localhost:8002" exited with 56.

https://travis-ci.org/github/chubin/cheat.sh/builds/741348053#L401

`--retry-all` makes `curl` retry on all errors, including connection resets.

Because even Ubuntu 20.04 version of `curl` is outdated

Because at least live reloading doesn't seem to work with `gevent`

Co-authored-by: Anatoli Babenia <[email protected]>

Ref. chubin#253

It is enough to monkey patch one time at the top level,
which is done in `bin/srv.py` web server script.

Sometimes there is nothing, sometimes lines are duplicated.

Duplicated lines problem appears, because Python root logger
handler and Flask's `werkzeug` logger handler both write the
same message. `cheat.sh` is hit, because it sets this root
logging handler.

Normally `werkzeug` doesn't setup its own handler if it sees
that there are some handlers that process its messages. This
in case of `cheat.sh` resulted in no stderr logging at all.
No Exceptions either. Because `werkzeug` catches the
exceptions and logs them.

Hovewer, sometimes `werkzeug` starts too early, befora app
is imported (pallets/werkzeug#1969)
and sets its logger anyway, before the app itself, resulting
in duplicating lines. In that case app root handler needs to
skip lines from `werkzeug`.

Kudos to @brandon-rhodes for `logging_tree` awesomeness

Co-authored-by: Anatoli Babenia <[email protected]>

This fix is temprorary, and must be implemented properly,
after Python 2 support will be fully dropped.

See https://github.com/dewitt/opensearch and
https://developer.mozilla.org/en-US/docs/Web/OpenSearch for more info.

Many more languages are supported than listed in the help file.

- Add link to jump to installation section
- Add link to jump to installing tab completion. Named this link "auto-complete" so that "auto" and "complete" (ending with an -e rather than -ion) would both show up when grepped/ ⌘+F

Why:

- Less intimidating to newcomers — I've just observed that friends/colleagues adopt tldr rather than cheat.sh soley because they didn't see the "get started" stuff up top. So they missed it.
- Faster to "just install it" when you know you're going to do that anyways. i.e. from a friend recommending. or on a new machine.

Helps with visual scannability when scrolling down the page

This is something we take for granted but newcomers to sh, Linux, and so on.

Also updates Stackoverflow user count from 9m to 14m. 
See https://stackexchange.com/leagues/1/alltime/stackoverflow

- Specific bash in some code blocks
- Specific zsh in zshrc config
- Fix unclosed `code` markup

Co-authored-by: Anatoli Babenia <[email protected]>

See chubin#285 (comment)

…hlorenz/doctoc  The documentation was so nice, I couldn't help but adding a toc.

    CHEATSH_UPDATE_TESTS_RESULTS=YES bash run-tests.sh