* list.h (SCM_LISTn): New macros. Make list creation in C code

* list.h (SCM_LISTn): New macros.  Make list creation in C code
prettier.  The idea comes from STk.

* sequences.h, sequences.c, append.h, append.c: Removed.  These
files implemented non-R4RS operations which would encourage
non-portable programming style and less easy-to-read code.

* Makefile.am (sequences.h, sequences.c, append.h, append.c):
Removed.

* libguile.h, eval.c, init.c, stime.c, unif.c: Removed #include
sequences.h, #include append.h.

* gh.h, gh_list.c: Renamed gh_list_length --> gh_length.

* list.h, list.c: Renamed scm_list_length --> scm_length, scm