move exmple/c/* to example/

example/c/cmake/CMakeLists.txt => example/cmake/CMakeLists.txt
example/c/lib_buffer_unpack.c => example/lib_buffer_unpack.c
example/c/simple_c.c => example/simple_c.c
example/c/speed_test_uint32_array.c => example/speed_test_uint32_array.c
example/c/speed_test_uint64_array.c => example/speed_test_uint64_array.c
example/c/user_buffer_unpack.c => example/user_buffer_unpack.c

Use `git log --follow example/filename` to see full log

Author: ygj6