chore: move __c_cpp/* to __ffi

__ffi/c_export/README.md

@@ -0,0 +1,29 @@
+
+Rust libray build:
+```
+cargo build
+```
+
+
+Python test:
+```
+python call_in_python.py
+```
+
+
+C test:
+```
+gcc call_in_c.c -L target/debug/ -lstringtools
+```
+
+
+NodeJS test:
+```
+npm install ffi
+node call_in_node.js
+```
+
+
+Reference:
+http://siciarz.net/24-days-of-rust-calling-rust-from-other-languages/
+