Add NameValueCollection extension methods

[jamiepollock]

Using this ticket to suggestion adding a collection of standard extensions for NameValueCollection. The intention is to mainly use this these with ConfigurationManager.AppSettings as AppSettinhs is a NameValueCollection.

• bool HasKey(string key)
• bool GetBooleanValue(string key, bool fallback)
• int GetIntegerValue(string key, int fallback)
• string GetStringValue(string key, string fallback)

As well as:

• IEnumerable GetIntegerValues(string key, StringSplitDelimiters delimiter)
• IEnumerable GetIntegerValues(string key, IEnumerable fallback, StringSplitDelimiters delimiter)
• IEnumerable GetStringValues(string key, StringSplitDelimiters delimiter)
• IEnumerable GetStringValues(string key, IEnumerable fallback, StringSplitDelimiters delimiter)

And possibly (WIP):

• T GetValue(string key, Func<string, T> method)

A PR will follow soon.