pyIRSF-2.3 released

Some major changes for sirpol.py have been made.

• Removal of the vertical stripe in the background of the Q, U, and V images
  by setting 'polstripe' = 1 in sirpol.param. The default value is 0.
  In most of the cases, most of the background of the Q, U, and V images are empty, zero
  and flat. In the algorithm, the median of each column of the image is calculated
  and the median value is subtracted from the column.

• All the frames were registered to the first frame of the set of observations
  both for SIRIUS and SIRPOL till the version 2.2.1. Shift and rotation among the
  frames within a wave-plate rotation cycle were corrected when making I, Q, U, V
  images for each of the cycle.
  A new option has been added since this version of pyIRSF. You can specify
  0 : not to register images among frames in each cycle
  1 : to register images among frames in each cycle but with only x-y shift taken
  into account
  2 : to register images among frames in each cycle with both the shift and rotation
  taken into account
  in sirpol.param.
  The option 0 yields a possible advantage of a better sky subtraction in
  making Q, U, and V frames.
  The option 2 cannot be used with 'polstripe == 1', that removes vertical stripes
  in Q, U, and V images, because the 'polstripe' algorithm assumes the background
  of the Q, U, and V image is uniform in the vertical direction. The uniformity gets
  broken by rotation of images.

• 'fix == 1' in sirpol.param did not work in the previous versions. The bug was fixed.

• Some refactorings were made.