Give read.amiramesh.header the option _not_ to parse the header

i.e. just return raw text
major speed-up in is.hxskel/hxlineset functions

* these were taking up to 50% of the time in a read.neuron call
* have now gone from 10-20 ms to ~ 0.5ms on my machine
Merge branch 'fix/amira-neuron-cleanup'

* fix/amira-neuron-cleanup:
  test and fix for reading hxlineset neurons without radius info
  disable test read of gzipped binary-encoded amira neuron
  new baseline data for hxskel test
  Exclude NeuronName from comparison when we are reading different files
  consistent rounding of amira format neurons with zapsmall
  Set NeuronName and other file fields when reading hxskel format neurons
  Give all.equal.neuron a fieldsToExclude argument
  stop returning NeighbourCount when reading hxskel neurons
  Add tests for equivalence of reading neurons in different amira formats
Merge branch 'feature/fast-is.amira'

This results in ~30% reduction in read.neuron time for amira neurons.
In general it will be necessary to keep an eye on the is.x functions in the
registry to ensure that they are sub-millisecond where at all possible.

* feature/fast-is.amira:
  major speed-up in is.hxskel/hxlineset functions
  Give read.amiramesh.header the option _not_ to parse the header