indentSpacer should be allowed to be 0

[ZevEisenberg]

The current code:

- (BONChainIndentSpacer)indentSpacer
{
    BONChainIndentSpacer indentSpacerBlock = ^(CGFloat indentSpacer) {
        NSAssert(indentSpacer > 0.0f, @"Indent spacer values must be greater than zero. Received %@", @(indentSpacer));
        __typeof(self) newChain = self.copyWithoutNextText;
        newChain.text.indentSpacer = indentSpacer;
        return newChain;
    };

    return [indentSpacerBlock copy];
}

However, there is no reason not to allow 0, because it will work, and it allows you to indent text that follows a space. Example use case: