INF: added a changelog and a script to generate it based on
commit messages  and tags
CODE: changed frequency points in constant module objects
BUG: fixed but in Frequency equallity tets
ADD: added f_unit option to io.general.read_all
CHG: changed number of points in frequency and waveguide objects in constants
CHG: allows Calibration to take dictionary for ideals/measured
    if dict is passed then sloppy_input is turned on, because
    the dict is unordered
ADD: added vi for Anritsu VectorStar and testcase
ADD: csv reader for anritsu vectorstar csv files
ADD: working on anritsu vectorstart vi,
CHG: mathFunctions.magnitude_2_db changed to set 0 to a big negative
CHG: network.two_port_reflect name now inserts a hyphen
ADD: working on anritsu vi
ADD: added to_dict() method of NetworkSet
ADD: add method Calibration.plot_caled_ntwks()
ADD: added error_ntwk support for two-port 7-term error model.

note that these two networks represent the hardware involved, but
cannot by themselves be used for de-embedding
ADD: networkSet.s_dict_to_ns to support calibration coefs
ADD: added network-type representation of calibration coefficients
	to Calibration.
CHG: changed Calibration.plot_coefs_db to call a more general
	method plot_coefs, which uses the Network plotting methods
	instead of re-implementing them
ADD: working on PNA and test case
ADD: working on PNA vna
ADD: working PNA and writing doc-strings.
DOC: vi.vna.PNA docs
CHG: mathfunctions.magntiude to dB, removed isneginf switch, need to
	test this better
ADD: skrf icon
TODO: need to setup tests for NetworkSet.
BUG: NetworkSet pickling doesnt work for dynamically generated
	methods. but Network.plot* does. need to fix this
ADD: network: new function to combine 4 oneports into a two port
ADD: network: function to operate on each parameters per frequency slice
CHG: vi working on PNA vi
ADD: generalized function n_oneports_2_nport
ADD: f_unit arg to Network.__init__
ADD: gen_three_port to create 3 port from set of 3 2-ports
ADD: added vswr to component func dict. not really the best way
to do it, but it was too easy