Update Axes3D.tricontour for custom triangulations

An example has also been added to illustrate the additional flexibility
possible with providing a user-defined triangulation.
Make Axes3D.contourf take arbitrary triangulations
Add Axes3D.contourf example
Update changelog/whats_new for 3D tricontour plots
Typos
Add EXPERIMENTAL note to Axes3D.tricontour[f] docs
color of candlestick lines

the line of a candlestick should have the same color as the body (rectangle)
Update of mlab.pca - updated docstring, added saving the eigenvalues.

The old version of pca class did not save the Eigenvalues - just the "fractions" that are just percentage values.

Also added info which row of Wt one can find the Eigenvectors.
axes_grid1: ImageGrid respect the aspect ratio of axes. This addresses #955
Remove she-bang line.
Use consistent imports
Remove unnecessary code comments.
Remove unnecessary calls to `show`
Rmove unused variable
Split up hist examples into two sections.

The original example was trying to do too much in one place.
Remove use of `setp` in favor of keyword args.
Replace multiple figures with subplots
Change bin edges to make the example clearer.
Add titles to clarify intent
Simplify example