Add .gitignore, mostly with binary files

This commit adds a .gitignore with unix and windows binaries, debugging
data from valgrind (dumps) and some folders.

The folders are: .build (the build-object folder), .vscode (Visual
Studio Code / VSCodium) and .private, a private folder to hold back some
files just for convenience.

.gitignore

@@ -0,0 +1,25 @@
+
+# Convenience Folder
+*.private/
+
+# Build data
+*.build/
+
+# IDE-/Editor - Data
+*.vscode/
+
+# Unix binaries
+*.a
+*.elf
+*.o
+*.so
+*.out
+a.out
+
+# Windows binaries
+*.dll
+*.exe
+*.lib
+
+# Debugging data
+*.vgcore