use | instead of l
remove across-line support because of multibyte char support
use customized matcher
refactor a customized matcher
improve function's name and remove an idle function
check a char under the cursor
sweep the buffer before testcases are executed
use command instead of function
use function istead of customized matcher, add some testcases

    check that f and F have the same context.
    check that nothing happens when the search fails.