Add cmake doxygen target and remove unused files (#315)

* Add cmake doxygen target and remove unused files

* Recovered deleted mainpage.dox file

* Add README.md explaining docs target

Author: PhilipFackler

CHANGELOG.md

@@ -37,6 +37,7 @@
 - Added support for DependencyTracking::Variable in PowerElectronics models.
 - Updated Jacobian value storage from `ScalarT` to `RealT`.
 - Added a header file defining constants to be used throughout the code.
+- Added `GridKitDocs` target for Doxygen documentation.
 
 ## v0.1
 

CMakeLists.txt

@@ -116,6 +116,9 @@ include(CTest)
 add_subdirectory(examples)
 add_subdirectory(tests)
 
+# Documentation
+add_subdirectory(docs)
+
 export(EXPORT gridkit-targets FILE ${CMAKE_CURRENT_BINARY_DIR}/GridKitTargets.cmake)
 
 # Configuring exporting cmake config