Basic implementation of plyr in NeuriteBlast
give NeuriteBlast a simplify argument (default T)

* user will be in charge of setting this when scores should not be simplified
* target use is when collecting distances/dotprops to make scoring matrices
Give nblast a ... argument
NeuriteBlast now uses ply for query and target loops

* this means that the outer loop (i.e. query) will be the one that is
  parallelised when query is a neuronlist
docs: more details about simplify argument
Merge branch 'feature/plyr'

* feature/plyr:
  docs: more details about simplify argument
  NeuriteBlast now uses ply for query and target loops
  Give nblast a ... argument
  give NeuriteBlast a simplify argument (default T)
  Basic implementation of plyr in NeuriteBlast
* closes #15