Discretize

- from pr 97
- update pypi credentials
- update appveyor and travis to auto-deploy to pypi on tags
- includes upload of wheel files from appveyor

- originally from pr: 36
- commits from: lheagy
- review from: rowanc1

3D Cyl Mesh
First implementation of a 3D cylindrical mesh. We discretize in r, theta and z.

Operators
- `edgeCurl`
- `faceDiv`
- `aveF2CC`
- `aveF2CCV`
- `aveE2CC`
- `aveE2CCV`

are all implemented and tested for second order convergence

Examples
There are some examples running this code in http://github.com/lheagy/casingResearch
- added a simple example that plots a 3D cyl mesh

Plotting
- add plot capabilities for plotSlice (and I think two slices through the mesh for `plotGrid()`)

Testing
- basic elements like the grids, counting of things.
- operator tests for mimetic properties


Other updates

Cell Grad Stencils are properties
- cell grad stencils are properties rather than methods. This pr will need to be followed by an update in the SimPEG regularization (addressed in simpeg/simpeg699)

minor updates
- plotting now uses the `C0`, `C1`, ... colors in matplotlib
- added `*.ipynb` to .gitignore

- from pr 92
- commits from micmitch
- review from lheagy

upgrades in plotSlice
- Added range_x, range_y, and sample_grid input arguments to plotSlice function.

- from pr 91
- make the stream_threshold compatible with plotslice

Just a few small changes for vtk mesh IO in python 3
- from pr 89
- commits from jcapriot
- review from lheagy

Cell grad operators for TreeMesh inversion
-----------------------------------------------

- from pr 72
- commits from: fourndo, micmitch, sgkang, lheagy
- review from: rowanc1, lheagy, jiajiasun

- First pass implementation for stencil operators
Initial implementation without hanging faces

- Second implementation with hanging faces

**Smoother gradients on Octree change.**

- Create gradient operators with dimensions for PDE problems.
- Add unit tests for operators. Thanks micmitch and sgkang

Solve DC problem in mine tunnels.
Tree mesh examples will follow shortly on SimPEG ... stay tuned.