handle braces escapes only

[drslump]

Since brace expansion usually happens before other expansions (i.e. glob), the current behaviour of handling all the escaped characters breaks later stages. For instance:

>>> braceexpand(r'{foo,bar}-\?')
['foo-?', 'bar-?']   # lost the information about the escaped "?"

I think it'll be best if escape handling only removed the backslash if it refers to a brace character, otherwise they're left in the expansions to avoid the information loss.

Since this would be a breaking change I guess the escape keyword arg could accept also 'preserve' to enable this mode?

Right now I'm working around it by double-escaping the string before feeding it to braceexpand:

>>> value = re.sub(r'\\([^{}])', r'\\\\\1', value)
>>> braceexpand(value)

But the approach is finicky since it only handles braces and won't work with something like {1\..5\,x}.

thanks for this great module!