Added str functions to provide name functionality to nodes.
Modified weights_load to look for from and to *names* rather than
indices. Thus deleted from and to ops from op.c and wop.[ch].
network_load now sets numerical from and to by resolving (and checking)
names. All this as yet untested!
Continued to code name features in weights and network. Tested with
feedforward.arc in example/network, looks good. Need to streamline what
is visible to users...
Extensive modifications to support the user-friendly file format detaile
din TODO. Modifications tested on example/network. Still to do: update
all examples to the new format and document it thoroughly. Review and
comment new code
Simplified the "named nodes and weights" business by making naming
compulsory. This made things simpler and more flexible.

TODO: Have the weights loader parse names with '-' and convert them into
from and to specifications!
Removed superfluous mint_sread_save_indices function
Simplified weights_load (lots of checks were unnecessary after mandating
node and weight names) and fixed a bug in handling of custom spread;
example/network now works correctly
Updated TODO list
Updated nodes save to new naming scheme. Nodes and weights now given
default names (n and w, respectively) if no name is found during
loading. Duplicate names are now automatically adjusted to resolve
conflicts (this is done also in network_add)
Started to move examples to named arc file format. Found some problems
with the interplay of operate functions, e.g., threads erases all
network operations (it made sense when the do_spread op was used). Some
redesign is needed.