Overloads with values for HoconRoot getters

[IgorFedchenko]

Related to #108

First, existing overloads like obj.GetDouble("a", @default: 5) did not work, because it was expecting underlying GetNode to return null when path was not found, but it was throwing exception (which is generally good thing, but here needed to catch it).

Second - there was no way to specify default value for collection getters (i.e. if I want to get empty list of ids if they are not set - the only options was to handle exception). Added this overloads, and added test for all of them.

[Aaronontheweb]

Hocon.Tests.HoconTests.GettingArrayFromLiteralsReturnsNull - have a failure on this spec.

[Aaronontheweb]

(I still don't know why Azure DevOps isn't showing status for PRs in this repository - only shows status for code once it's directly merged into dev)

[IgorFedchenko]

Hocon.Tests.HoconTests.GettingArrayFromLiteralsReturnsNull - have a failure on this spec.

Yup, the behavior asserted in this test was incorrect actually, so fixed it too

[Aaronontheweb]

@IgorFedchenko looks like the CI system is not our friend still

[IgorFedchenko]

@IgorFedchenko looks like the CI system is not our friend still

@Aaronontheweb Yup... In Akka.NET also not all steps are completed. Looking at issue here, they still did not resolve this problem.

[Aaronontheweb]

Hocon.Extensions.Configuration.Tests.ConfigurationSpec.ShouldReloadConfigurationOnFileChange failed - this test seems to be pretty racy (has a high flip rate on Azure DevOps.) I'll take a look at it.

[Aaronontheweb]

@IgorFedchenko have a merge conflict here

[IgorFedchenko]

@IgorFedchenko have a merge conflict here

Since #148 was based in this PR, the changes are already in dev branch, and #148 overwrites some of them.
Anyway, resolved conflicts now, should be ready for merge.

[Aaronontheweb]

Thanks @IgorFedchenko