Refactor CMake

This is a minor release. It includes

• Complete overhaul of CMake build configuration
  • Increases SUNDIALS dependency to >= 5.5
• Bug fixes
  • Fix bug in initialization of slack bus
  • Fix bug in adjoint example

Added power flow analysis

New features in this commit:

- Parameter estimation example
- Power flow model composer with test example
- Improved CMake build
- Updated documentation