functions/modules for unit test

[yunjunz]

Put up an issue here for the discussion on the unit test.

core algorithms

• ifgram_inversion.ifgram_inversion_patch(), which calls estimate_timeseries()
• dem_error. correct_dem_error()
• utils.utils1.run_deramp()
• timeseries2velocity.run_velocity_estimation()

objects (and their member functions)

• objects.resample()
• objects.timeseries()
• objects.ifgramStack()
• objects.connectComponent()

utility functions

• utils.readfile.read_hdf5_file()
• utils.readfile.read_binary_file()
• utils.readfile.read_attribute()
• utils.writefile.write()

Functions within utils.utils0 and utils.utils1 are important too, but I will re-organize them into more meaningful sub-modules in the next release, so their location will be changed. I guess we can skip them for now.