Simpeg

- from pr: 758
- commits from: lheagy
- review from: thast

- soft removal of python 2.7: we don't explicitly break compatibility as in 731, but it is no longer tested on Python 2.7
- added a note in the docs saying we will not be working to ensure compatibility with python 2.7 anymore

DC Fields Derivatives
- from pr 724
- commits from: lheagy
- review from: sgkang

DC Resistivity
- add fields derivatives with respect to the electric field (in case you want to invert e-field data)
- add e-field receivers to DC problem
- see for example: https://github.com/simpeg-research/heagy-2018-injection-inversions

TDEM
- add charge and charge density to j-fields
- bug fix in calculation of db/dt in the j-fields object
- add grounded source that solves the mmr problem in the H-J formulation for permeable targets

Directives
- add option to save output to a directory, the default is the current working directory

numpy matlib imports
- from pr 755
- commits from: lheagy
- review from: thast

import matlib explicitly as in numpy 1.16, it isn't imported in the numpy namespace be default


- from pr: 670
- commits from: fourndo, thast
- review from: thast , lheagy

A couple of improvements or fix for Potential Fields:

- Fix reading functions for UBC file format (in case of line break)
- add `ModelMap` property
- Change `survey.nD` definition so it is independent of `Problem`
- Use `reg.deriv2` instead of `reg.W` for computing the preconditioner in `Directives.updatePreconditioner`
- general PEP8 improvements (powered by AutoFormat)
- naming convention: `readUBCgravObs` becomes `readGravityObservations` (for consistency between `Grav` and `Mag` names conventions.)
- Combine all Mag problems (susc, amp, MVI) under Magnetics.MagneticIntegral
- Change coordinate system from legacy x, y, z(down) to convention x, y, z (up)
- Add test+example for MVI-S on TreeMesh
- Add test+example for Amplitude inversion (CSM algo)

- from pr 749
- commits from lheagy
- review from thast

update plot2Ddata
- update logic in plot2Ddata so that two vmin, vmax values cannot be provided to contourf (e.g. it was previously possible that an explicit vmin, vmax was provided by the user and that a vmin, vmax was chosen based on the colorbar)
- ensure that if both clim and vmin, vmax provided to contourOpts that they are identical

fix std in DataMisfit and possible bug in PlotUtils

- from pr 745
- commits from thast
- review from micmitch, lheagy

Fix for Issue 746

- fixed `DataMisfit.std` that now take into consideration `survey.std`. So you are not forced to set `DataMisfit.W` manually anymore

- Fixed: `Survey.MakeSyntheticData`, if not given a `std`, was overwriting `survey.std` even if already set. Now it will use `survey.std` if not given a `std` argument.

Explanation:
`DataMisfit.std` was set to 5% by default, but to change it to `survey.std`, it expected a `None` value, thus it never gets updated...

- bonus: light improvement again of `Plot2DData` (reordering of `if` statement so specifying `contourOpts['vmin','vmax']` without a `clim` works.

- bonus: Somehow PR 725 did not make it to improve `plot_misfit_curves` so I put it back here. Mainly, more option to plot $\phi_m$ or $\phi_small$ and $\phi_smooth$ independently, plus more options to save the figure.


Code of conduct
- from pr 744
- commits from lheagy
- review from rowanc1

Add a code of conduct based on the contributor covenant to SimPEG

fixed possible issue for levels definition in `SimPEG.Utils.plot2DDdata`
- from pr: 738, closes 734
- commits from: thast

Description
- fixed possible issue for levels definition in `SimPEG.Utils.plot2DDdata`
- add mask functionality (already proposed as args but not implemented)
- choice of linear or nearest interpolation
- check if there is already a vmin, vmax in the contourOpts dict before adding them based on user-input clim
- improved example for`SimPEG.Utils.plot2DDdata`
- add an example for the IO.pseudosection function

Example output:


Installation docs
- from prs: 736, 737
- commits from: sdevriese, fourndo

Description
- Replace links to numpy example page with link to SimPEG examples
- update link for anaconda


Do not install tests in site-packages
- from pr: 740
- commits from: cgohlke

Description
- exclude tests from from SimPEG installation