Rename structures to typedefs:
* FileOpContext -> file_op_context_t
* FileOpContextUI -> file_op_context_ui_t

Signed-off-by: Slava Zanko <slavazanko@gmail.com>
use UTF8_CHAR_LEN instead of a magic number

Signed-off-by: Slava Zanko <slavazanko@gmail.com>
Reduce cppcheck warnings (style) in src subdirectory.

Signed-off-by: Slava Zanko <slavazanko@gmail.com>