I have renamed the library "seq" instead of "sequences".

This patch also adds the following functions: seq-take-while,
seq-drop-while, seq-remove, seq-count, seq-do (as an alias to mapc),
seq-each (same alias), seq-map (as an alias to mapcar), as well as the
seq-doseq macro, similar to dolist.

If you think that some important functions are missing, please tell me.

I didn't add documentation yet, as I don't really know if it should be
in the Sequences section of the Elisp manual or somewhere else.

Cheers,
Nico