Various fixes to manual text.

Cleaned up some references, grammar, etc.

More minor changes

Fixes in manual

More changes

Various and sundry

Fixing math formatting

Adjusted units to :math: format for cleaner look. No more ^ in units,
still more to go

More unit fixing

Fixed units, copy editing

Averaging section edited

So many units fixed.

Geotherm done

Fixed various geotherm units and citations

Typo

typo

typo

typo

Fixed underline typo

Underline typo fixed

Fixed label

Fixed label in equation

Added note about B&S depth limit

Added note about B&S depth limit

Fixed from 2700 km to 270

Fixed from 2700 km to 270
Merge pull request #53 from lordkman/Cay_man

Cleaning up manual slowly but surely.