matplotlib Code

Replace tabs with spaces.

fixed some doc formatting errors

Remove trailing whitespace.

Update CHANGELOG and api_changes for the changes to psd and friends.

Add a converted MatLab example that was used to figure out the differences between MatLab and matplotlib PSD scaling.

Update spectral methods (psd, csd, etc.) to scale one-sided densities by a factor of 2 and, optionally, scale all densities by the sampling frequency. This gives better MatLab compatibility. Update corresponding Axes methods, and make Axes.psd() label the y-axis of the plot as appropriate.

fixed inaxes event bug

Correct typo in comment.

Updated changelog.

fix drawlsmask so it works for cylindrical projections that have limits
outside -180,180