✨ Richify, add integrations with Rich everywhere

[tiangolo]

✨ Richify, add integrations with Rich everywhere.

This started with a copy of https://github.com/ewels/rich-click, and started evolving from there with several refactors.

Rich is still an optional dependency, but when installed, it's used in several places.

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This PR includes several things related to the new deep integration with Rich.

Use standard print

Now typer.echo() is no longer recommended, for the simplest cases, standard print() is recommended and documented.

And for more complex cases, Rich is recommended. Several places in the docs have been updated to recommend Rich, e.g. the whole section for "Printing and Colors".

Rich for --help

When Rich is installed, it's used to format all the output of --help commands.

New docs for deprecated

New docs for the deprecated parameter in commands, it includes special formatting and handling with Rich.

Rich Markup and Markdown

Rich Markup and Markdown can be enabled with a new parameter rich_markup_mode that can be None, "rich", "markdown".

Including a new section in the docs for it.

When using "rich" the content in help strings, epilog and docstrings is parsed with Rich Markup, when "markdown" is used, then it's parsed with Rich Markdown.

Help Panels

There's a new parameter rich_help_panel in typer.Typer(),app.add_typer(), app.command(), typer.Argument(), and typer.Option().

Setting it to a name will render that component in a Rich panel in the help from the --help option.

New docs for that in the sections about help for CLI arguments, CLI options, and commands.

Epilog docs

New docs for using the epilog, also rendered with Rich.

Tests

Updated tests and many new tests to keep 100% of test coverage with the new Rich utils and integrations.

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[codecov]

Codecov Report

Merging #419 (f5d2e47) into master (8212e73) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master      #419    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          260       280    +20     
  Lines         5486      6406   +920     
==========================================
+ Hits          5486      6406   +920     

Impacted Files	Coverage Δ
tests/test_completion/test_completion_install.py	100.00% <ø> (ø)
tests/test_completion/test_completion_show.py	100.00% <ø> (ø)
...test_parameter_types/test_bool/test_tutorial001.py	100.00% <ø> (ø)
...st_parameter_types/test_number/test_tutorial002.py	100.00% <ø> (ø)
...test_parameter_types/test_uuid/test_tutorial001.py	100.00% <ø> (ø)
typer/params.py	100.00% <ø> (ø)
typer/utils.py	100.00% <ø> (ø)
docs_src/arguments/default/tutorial001.py	100.00% <100.00%> (ø)
docs_src/arguments/default/tutorial002.py	100.00% <100.00%> (ø)
docs_src/arguments/envvar/tutorial001.py	100.00% <100.00%> (ø)
... and 208 more

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[CarlosBergillos]

@tiangolo Hi!

Sorry if this is not the right place to ask this, but how did you generate the html for the Rich terminal outputs for the docs? (as added in this PR, and this commit 501f3a9).
The outputs with <b>, <font color="#F4BF75">, etc.

I'm interested in adding similar html outputs to the docs of a personal project that uses typer.

Thanks!