feat: exec parser for desktop entries (#78)

Feature-rich Exec= parser implementation for .desktop files
* backslash stripping (e.g '\ ' -> ' ')
* percentage stripping (e.g '%u' -> '', '%%' -> '%')
* quote string handling (e.g 'arg1 "arg 2"' -> "arg1", "arg 2")
The current implementation strips all "percentage codes", instead
of handling them.
Argument count is limited at 100.

---------

Co-authored-by: javalsai <jvssxxi@gmail.com>

include/desktop_exec.h

@@ -0,0 +1,7 @@
+#ifndef DESKTOP_EXEC_H_
+#define DESKTOP_EXEC_H_
+
+int parse_exec_string(const char* exec_s, int* arg_count, char*** args);
+void free_parsed_args(int arg_count, char** args);
+
+#endif