Add vector LaTeX command (\vec)

The vector command places a right arrow above the text name of the vector.
This commit models the rendering of LaTeX where the arrow does not
extend to the full width of the vector name.
EtherPad discussion way, way out-of-date

and is being (unintentionally, by people who don't know how to use
Etherpad?) vandalized. It's been archived at the "v0.3 Architecture"
wiki page.
Cleanup based on @laughinghan feedback.

Remove redundant method name assignments.
Fix indentation (tab to spaces) in stylesheets.
Remove extraneous CSS properties from ruleset.
Merge pull request #185 from devlin/add_vector

Add \vec, using the Fraction technique of display:block and line-height
Merge branch 'master' into dev