Convenience methods as discussed in #84

[mbcrawfo]

Adds convenience methods for accessing a key using a single string that has section and key name combined, eg "section:key". Separator char is defined in the parser configuration. Will close #84

[rickyah]

Sorry, it took me so long to answer due to a combination of holidays and a peak of really hard work.

I'll review this in no time, maybe I'll add a little change: change the section - key separator character to a dot and make it not customizable.

That character just don't belong on the parser configuration (that character is not used in the parsing) and I don't really see the need to customize it when is just a helper method to access keys inside a section in a easier way, but maybe I'm missing something.
Changing it to a dot is just because looks better IMHO; we are all used to reference inner properties/fields with a dot: data.GetKey("MySection.myKey") What do you think?

I'll try to merge it today, thank you very much @mbcrawfo!

[mbcrawfo]

I would argue for keeping the separator character customizable in some way, since it's hard to predict what kind of crazy naming people might be using in their ini files. Maybe just make it a property of IniData? Otherwise sounds good to me!

[rickyah]

You are right, I did not take into account section names like [section.1] I'll put it in IniData then.