BlackrockRawio really hard to read.

[samuelgarcia]

The actual BlacrockRawIO have been written with sevral stratum and several dev along time.
This make the actual state of blacrockio really hard to read and patch.
This is mainly my fault because when I migrate this IO to rawio I kept many internal methods intact.

@JuliaSprenger @mdenker @bjoern1001001 @lzehl : if you don't mind I would plan a refactor of this IO after proxy object.

A list to be discussed:

• dictionary of function depending on version make very hard and many code jump to
  follow the main logic. In my point of view, I would prefer one unique clear method (function) like
  read_nsx_header with a if ver=='2.1' ... elif ver=='2.2' inside rather than this dict to functions.
• Move the read header stuff to functions instead of methods. I do this in many
  IO. It is easier to debug because you can test read_nsx_header(filename) independently from the
  main class logic.
• variable changes:
  • nsx_nb to nsx
  • data_bl to seg_num
  • spec to version

Tell me.

Samuel