DWDS/Dialing Concordance Code

+ got replacement #left/#right sort operators basically working
- added token-attribute field argument to #left/#right (analagous to #less_by[BIBL,LO,HI])
- added lower-/upper-bound arguments to #left/#right (analagous to #less_by[BIBL])
+ implemented new offset-based context-sort operators #(asc|desc)_by_context
- #left and #right are now basically just aliases for #asc_context with offsets -1,+1
- TODO: improve syntax and make #left/#right real aliases
- TODO: add break-collection bounds-checking to context-sort operators
+ un-method-fied string_socket.h functions (since they're also used by ddc_search pseudo-cgi)