read.neurons signals problem file and warns immediately

* fixes #61
* includes test for signalling the problem file
fix bug in reading amiramesh binary files with empty sections

* warning because there was no linefeed but rather an immediate null from next
  block of data
* so far this never resulted in any errors, but looks like it could have done
  in situations where next byte was not 0
* fixes #63
Test identity of neurons read in by read.neuron and read.neurons

* ensure that they are really identical by looking at everything except
  the CreatedAt field