fix(config): print only the value of config get and add display preferences

tea config get printed "key<TAB>value", so $(tea config get editor) was
not usable; it now prints the value alone, and --show-source appends the
source (D18). config get reads the instance's user, and instance settings
come from the selected instance (--host, TEA_HOST, default_host or the
sole instance). Unknown keys list the valid ones, and keys that need
--host or --user say so. config path no longer loads the settings, so it
works when hosts.yml is broken. config list is a table on a terminal.
config set confirms the change on a terminal and warns when default_host
has no account.

config.yml stores the hyperlinks (auto, always, never) and markdown
(auto, raw) preferences that tables and views now read, instead of the
TEA_HYPERLINKS and TEA_MARKDOWN variables. The environment table moves
out of tea config --help into tea help environment.

alias set refuses to replace an alias without --clobber, drops a leading
"tea", and explains how to quote an expansion with spaces or flags.
alias delete takes several names or --all, alias list is a table, and
an empty list says so on a terminal.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/human_output.go

@@ -30,8 +30,7 @@ func (a *application) colorEnabled() bool {
 	return terminal.ColorEnabled(preferences.Color, a.deps.Streams.OutTTY, a.deps.Getenv)
 }
 
-// display describes stdout for tables and views. The hyperlinks (auto, always, never) and markdown
-// (auto, raw) preferences are read from TEA_HYPERLINKS and TEA_MARKDOWN until config.yml stores them.
+// display describes stdout for tables and views under the color, hyperlinks and markdown preferences.
 func (a *application) display() terminal.Display {
 	preferences, _ := a.preferences()
 	streams := a.deps.Streams
@@ -39,8 +38,8 @@ func (a *application) display() terminal.Display {
 		TTY:       streams.OutTTY,
 		Color:     terminal.ColorEnabled(preferences.Color, streams.OutTTY, a.deps.Getenv),
 		TrueColor: terminal.TrueColor(a.deps.Getenv),
-		Links:     terminal.HyperlinksEnabled(a.deps.Getenv("TEA_HYPERLINKS"), streams.OutTTY, a.deps.Getenv),
-		Markdown:  terminal.MarkdownEnabled(a.deps.Getenv("TEA_MARKDOWN"), streams.OutTTY),
+		Links:     terminal.HyperlinksEnabled(preferences.Hyperlinks, streams.OutTTY, a.deps.Getenv),
+		Markdown:  terminal.MarkdownEnabled(preferences.Markdown, streams.OutTTY),
 		Width:     streams.Width,
 		Now:       a.deps.Now(),
 	}