Add dir_file and expand commands

Output file names matching patterns in directories.
Add the head command

Yield only a given number of lines, then stop.
If size=None, yield all the lines of the stream.
Add the tail command

Yield  the given number of lines at the end of the stream.
If size=None, yield all the lines. If size!=None, it will wait for the data
stream to end before yielding lines.
Add the traverse, wc and glue command

traverse : Recursively browse all items, as if nested levels where flatten.
Yield all items in the corresponding flatten list.

wc : Return a list indicating the total number of [lines, words, characters]
in the whole stream.

glue : Join every lines in the stream, using the given delimiter.
The default delimiter is a space.