Review SGR capabilities of clients; add support and notes

[DavidRieman]

It might be interesting to see if any clients (or clients in certain contexts, like a raw telnet app inside specific terminals) support some of the ANSI SGR codes that we don't have encoded in AnsiSequences.cs yet. If some of them seem useful, we could provide some more of these (and perhaps some comments about rough levels of support). For example, if we find contexts where SGR 26/50 get honored, it would be good for MUD contexts which have a mix of fixed-width needs and readability needs (such as drawing an ASCII map on the left side but allowing ample space on the right for proportional font manually word-wrapped with room description, or chat, or whatnot)... Having these codes available for usage would be helpful.

For reference: https://en.wikipedia.org/wiki/ANSI_escape_code