Check terminal supports formatting

[TomJGooding]

Today I learned while checking out Textual's new Markdown feature that urxvt apparently doesn't support strikethrough formatting!

Here's a few simple bash commands to check whether your terminal supports text formatting:

echo -e "\e[1mbold\e[0m"
echo -e "\e[3mitalic\e[0m"
echo -e "\e[3m\e[1mbold italic\e[0m"
echo -e "\e[4munderline\e[0m"
echo -e "\e[9mstrikethrough\e[0m"

Hopefully this helps someone else with similar issues!