Allow { and }

[serin-delaunay]

cheapbotsdonequick.com says they can now be escaped as \\{ and \\}. Example grammar:

{
	"origin": ["\\{\\}#{}#"],
        "{}": "no problem!"
}

Not sure if that's a new feature or not, but they can be added as special cases in MarkovTracery.py (char_renderings, char_symbols might not be necessary).
Also, remove the proscription against them in index.html.

[serin-delaunay]

It's not possible after all to use arbitrary strings with { and }. See this grammar, for instance:

{
	"origin": "\\{ \\} \\{ \\}"
}

Closing until this is fixed in CBDQ.