Verbatim copy of CMTKStatistics from nat.as

* test required slight modifications of course
rename to cmtk.statistics
remove exe argument and roxygenise
fix typo in help
Teach cmtk.statistics to pass ... to cmtk tool

* use cmtk.call internally to prepare the system call
Merge branch 'feature/cmtk.statistics'

* feature/cmtk.statistics:
  Teach cmtk.statistics to pass ... to cmtk tool
  fix typo in help
  remove exe argument and roxygenise
  rename to cmtk.statistics
  Verbatim copy of CMTKStatistics from nat.as
* part way to closing jefferislab/nat.flybrains#16
Bump version to 1.5.11