Suppress the usage of ANSI color when indicated by the user

When `$TLDR_MAN_NO_COLOR` or `$NO_COLOR` is present and not an empty
string, prevents the usage of ANSI color.

For more, see <https://no-color.org/>.

src/tldr_man/main.py

@@ -27,7 +27,7 @@
 
 from pathlib import Path
 from contextlib import suppress
-from os import remove
+from os import remove, getenv
 from functools import wraps
 
 import click
@@ -128,7 +128,11 @@ def subcommand_manpath(locales, page_sections):
     print(':'.join(unique(str(man_dir.parent) for man_dir in pages.get_dir_search_order(locales, page_sections))))
 
 
-@command(cls=HelpColorsCommand, help_headers_color='yellow', help_options_color='green', no_args_is_help=True)
+@command(cls=HelpColorsCommand,
+         help_headers_color='yellow',
+         help_options_color='green',
+         context_settings={'color': False if getenv('TLDR_MAN_NO_COLOR') or getenv('NO_COLOR') else None},
+         no_args_is_help=True)
 @argument('page', nargs=-1, required=True, shell_complete=page_shell_complete)
 @option('-p', '--platform',
         metavar='PLATFORM',

tldr-man.1

@@ -159,6 +159,9 @@ The location of the page cache directory. This directory is created by the
 command and is accessed by other commands.
 If this variable is not set or is not an absolute path, this defaults back to the value of
 .BR $XDG_CACHE_HOME/tldr-man .
+.TP
+.BR TLDR_MAN_NO_COLOR ", " NO_COLOR
+When present and not an empty string (regardless of its value), prevents the usage of ANSI color.
 .SH "FILES"
 .TP
 .BR $XDG_CACHE_HOME/tldr_man
@@ -183,6 +186,10 @@ TLDR\-Pages Client Specification
 .UR https://standards.freedesktop.org/basedir-spec/basedir-spec-latest
 XDG Base Directory Specification
 .UE .
+.PP
+.UR https://no-color.org/
+NO_COLOR
+.UE .
 .SH "EXAMPLES"
 .PP
 Display the tldr\-page for