.gitignore: Add.
L2U/Handlers.pm: Modify Unicode representations used in \frac and \dot handlers.
L2U/Constants.pm: Add (a few) more subscripts.
t/*: Adapt to changes of frac- and dot-handlers.

Also, add a few newlines for purposes of readability, eh?
t/celebrities.t: Add Euler-Lagrange equation.

... shining beacon of beauty that it is.

Also, finally introduce a more digestible form of writing test
expectations down.