added search_before()
added support for a temporary test file, test2.c  makefile etc.

changed NODE_ERR to NODE_INT (and member 'err' to 'num')
commented most functions
updated traverse to return an error code, and others to check for it
makefile has 'gitindex' target, to add all code to git's index
makefile automatically converts spaces to tabs before compiles and gitindex
added .gitignore

add tabify target to convert all spaces to tabs
made run the default target

add delete_list()
separate print_node(NODE* head), which prints the data of head, and
  print_node_at(NODE* head, int pos), which traverses head to index pos, then
  prints that node

moved the portions of search() that call printf to psearch(), so that it can be
used silently