move HL_* variables to syntax.h
move VALID_* defines to buffer_defs.h
move b_flags definitions to buffer_defs.h
move BF_WRITEMASK to buffer_defs.h
move WILD_* defines to ex_getln.h
move EW_* defines to path.h
move FINDFILE_* defines to file_search.h
move SST_* defines to syntax_defs