New feature: Building individual package tree from each dep (in sandbox)

[averissimo]

Goal of functions: ensure that individual dependencies build for the declared versions (it does not perform any checks on the parent package)

This could be added as an auxiliary strategy, I didn't went all in without first start a discussion

Overview of changes

Useful code I developed to find out minimal version that builds successfully

• Supports reading a package DESCRIPTION and attempts to install each dependency independently
  • Using the declared version
• Finds first version of package that builds successfully by iterating over versions from CRAN archive
  • both from the initial version or with a version rule (>= 2.0)