[PHYS 2214] Started prelim2 notes.
Added dispersion to notes

I'm editing from github, so excuse anomalies.
[PHYS 2214] Added dope beats section.

Even Dr. Dre is jealous.
[PHYS 2214] Added Doppler section
[PHYS 2214] Added energy transport in mech. waves

A quick explanation of potential energy density that I elided from the
notes.

U_k = 1/2 * tau * Dx * (dy/dx)^2
    = 1/2 * tau * dy/dx * dy * Dx/dx
    ~ 1/2 * tau * sin * dy
    ~ 1/2 * tau_y * dy

This resembles a force in the y-direction times the displacement which
is work which is energy. And indeed the displacement in the y direction
is the source of the elastic potential energy. However, the 1/2 seems
suspect. The Dx/dx =~ 1 is not real math (at least not as far as I
know). I didn't enter it in the notes as I don't find it too helpful,
and in fact can be harmful. I enterred it here so it won't be lost
forever.
[PHYS 2214] Finished mech. wave energy section.

I forgot to add total energy from the previous commit.
[PHYS 2214] Added mechanical wave power.

Existential and universal quantifiers ftw.
[PHYS 2214] Makefile is more makey.

Running `make build` twice doesn't build twice anymore.
[PHYS 2214] Added energy in sound waves.

The derivations in the notes were sparse for sound waves. Up next is the
beast power section.
[PHYS 2214] Added power on sound.

I got lazy. The notes are terse.
[PHYS 2214] ``Finished'' notes.

The prelim is tomorrow and it is 4:22 AM. I rushed through the notes to
finish them. The derivations near the end become hairy and arguably not
too instructive, so their elision shouldn't be too worrysome.
Added pdf
Merge pull request #2 from mwhittaker/PHYS-2214-prelim2

PHYS 2214 Prelim 2 Notes