Getting rate for the last working day

[matma]

Hello,
When You have a document where a date isn't working date, You should still be able to get avg. rate for it. So I changed the code to do this.

It's an option:
NbpExchange::Config::get_rate_from_last_working_date = true

The next step is to calculate holidays (using https://github.com/alexdunae/holidays gem)

Pozdrowienia :)

[sparrovv]

I was thinking on doing this, but for my needs the previous version was enough, but I'm happy, that someone is using it:)

Basically I like this pull request, but I would encourage you to change some method naming, like:

get_rate_from_last_working_date -> rade_from_last_working_date
is_valid_date? -> valid_date? (question mark = is, at least for me)

It's more ruby style:)

[sparrovv]

What do you think about changing this line to:

while not valid_date?(date)
or
while !valid_date(date)
?

[matma]

Ok, I will change this - I'm still learning Ruby. My main language is C# so please be tolerant ;)