Specify usable escape sequences in Exception#detailed_message

An error message is primarily rendered in a terminal emulator, but is
also shown in a browser by converting it to a HTML fragment.
However, the conversion would be unreasonably difficult if the message
includes any escape sequence (such as cursor move or screen clear).

This change adds a guideline about escape sequences in
`Exception#detailed_message`:

* Use widely-supported escape sequences: bold, underline, and basic
  eight foreground colors (except white and black).
* Make the message readable if all escape sequences are ignored.

0 files changed, 0 insertions, 0 deletions