sanitize nickname input

[GiselleSerate]

Currently I'm leaving the input checking very basic; you just can't use special characters. I think some of them are permissible in alias, though, so you should:

• [x] figure out which characters are okay in alias
• [x] add the above to the permissible character set

[GiselleSerate]

• @, #, ^, *, -, _, +, ,, ., ?, {, }, [, ] get saved. Permissible characters. Don't remove these.
• ', " don't get saved, but calling the alias with quotes in it preserves behavior as long as there are matching quotes within the alias. Can be handled if left in, or not.
• \ doesn't get saved, but if you call alias with \ the line it returns can be handled properly. Can be handled if left in, or not.
• !, &, (, ), =, /, :, ;, <, >, | break the normal alias command, so we can call those undefined behavior. Don't worry about these characters.
• $ substitutes in the variable that bash thinks follows $. This is a problem.

Strategy: stop sanitizing, it's fine. The only problem is substituting in variable names.

EDIT: It's actually not a problem. If someone wants a $ in their alias, they need to quote it.

[aryarm]

And alias doesn't allow $ signs in nickname, I think. "The characters /, $, `, = and any of the shell metacharacters or quoting characters listed above may not appear in an alias name." (according to the manual?) So alias 'hi$bro'='desk' won't work.

[GiselleSerate]

Yeah, I think the only thing that we might need to worry about are variable substitutions.