BCL API review: Rename GetCofigurationSection() and GetConfigurationSections() methods on IConfiguration

[divega]

The current names contains redundancy and aren't very clear. Here are some suggested changes we believe help improve on that:

• GetConfigurationSection() changes to GetSection()
• GetConfigurationSections() changes to GetChildren()
  • argument of GetChildren() overload should be parentKey

[tlc-sundown]

Sometimes we talk about sections, sometimes about children. Can we not define once and for all what we're talking about ?

• GetConfigurationSection() changes to GetChild()
• GetConfigurationSections() changes to GetChildren()

or

• GetConfigurationSection() changes to GetSection()
• GetConfigurationSections() changes to GetSections()

[divega]

This was done in beta7 in ddd7c42. It is now superseded by #269 which talks about further changes.