fixed bug in mtplottools if there is no z_err input, error in determinant is set to ones, added function to discretize color maps in mtcolors
corrected errors in the reading of spectra-type edi files - problems with underscores in tippererr removed

Signed-off-by: LK <LK@uni>
Merge branch 'master' of github.com:geophysics/mtpy
edi.py : reading spectra data - corrected missing blank space between concatenated lines of spectra entries

Signed-off-by: LK <LK@uni>
fixed bug in plotresponse when plotting skew angle
fixed bug in plotresponse when plotting phase tensor, size is now correct
fixed bug in plotresponse when plotting xlabels are now correct
fixed bug in plotnresponses when plotting phase tensors, size is now correct
changed the ResidualPhaseTensor to I-pt1^-1*pt1 and added attribute residual_pt which is a PhaseTensor object so you can calculate skew, azimuth, etc.
changed tipper_err (imaging convention) to tippererr (core convention)

Signed-off-by: LK <LK@uni>
IMPORTANT: changed error defintion of the phase: "relative phase error" is always in perspective to the respective relative error of the resistivity, i.e. if the rel error of rho is 10% then the rel. error of the amplitude of Z is 5%, and that defeines then a value for the phase angle !! see files z.py and calculator.py"

Signed-off-by: LK <LK@uni>
Fixed residual phase tensor so the attribute residual_pt is correct and is a PhaseTensor object.
added a new colormap to mtcolors
z.py - corrected rotation_angle from list to array, so "value - z.rotation_angle" makes sense

Signed-off-by: LK <LK@uni>
accidentally left a debugging "sys.exit" in the master - corrected this

Signed-off-by: LK <LK@uni>
changed last instances of tipper_err to tippererr

Signed-off-by: LK <LK@uni>
fixed bug in ws2para.py where the station and resistivity files where written to the same file
Merge branch 'master' of https://github.com/geophysics/mtpy into jp.ws3d
working on documentation