Bug fix and new methods

Bug Fix

• gaussian_filter did not work in previous version because of slightly different implementation of other running-kernel filters.
• impy.zeros did not work because I forgot adding it in __init__.py.
• clip_outliers and rescale_intensity did not work in some cases because of bad implementation.

New Methods

• gaussfit_particle
• structure_tensor_eigval
• structure_tensor_eig
• dog_filter
• peak_local_max

Changes

• Following methods now support new keyword argument update : bool -- mean_filter, median_filter, gaussian_filter, tophat, erosion, dilation, opening, closing. If update=True, the original image is updated just like filters in ImageJ.
• Gaussian functions are integrated in gauss.py and now it can be utilized for generating images and fitting to single molecules.