Alias bridgmanite to perovskite due to the new naming
Merge pull request #27 from ian-r-rose/add_bridgmanite

Alias bridgmanite to perovskite due to the new naming
Add initial versions of tutorials
Work on tutorials
Edits
Add a bunch of text for step_1
Add lots of text, modifications for step_2
Text for step_3
Adjustments, text
minor text changes

changed 'mantle' to 'lower mantle'
and added formula for stishovite and wuestite
% to Fraction in figure label
More text
Don't need to return mineral.
Split up onto two lines