chore(git): add Doxygen file

NOTE: Doxygen isn't yet used in the engine, however I do plan to use it
in the future

Doxygen

@@ -0,0 +1,35 @@
+PROJECT_NAME           = "ICEngine"
+PROJECT_NUMBER         = "ALPHA-2.0.0"
+OUTPUT_DIRECTORY       = docs-gen
+EXTRACT_ALL            = YES
+EXTRACT_PRIVATE        = NO
+EXTRACT_STATIC         = YES
+
+INPUT                  = src/ include/
+FILE_PATTERNS          = *.cpp *.h *.hpp
+RECURSIVE              = YES
+
+# Default to html
+GENERATE_HTML          = YES
+GENERATE_LATEX         = NO
+GENERATE_MAN           = NO
+
+INLINE_INHERITED_MEMB  = YES
+FULL_PATH_NAMES        = YES
+
+EXTRACT_NAMESPACE      = YES
+EXTRACT_LOCAL_CLASSES  = YES
+EXTRACT_ANON_NSPACES   = NO
+SHOW_INCLUDE_FILES     = YES
+
+OPTIMIZE_OUTPUT_FOR_C  = YES
+GENERATE_AUTOGEN_DEF   = NO
+
+WARNINGS               = YES
+WARN_IF_UNDOCUMENTED   = YES
+WARN_IF_DOC_ERROR      = YES
+
+SORT_MEMBER_DOCS       = YES
+SORT_GROUP_NAMES       = YES
+
+ENUM_VALUES_PER_LINE   = 1