Rewrite introduction to asymptotic material

Rewrites the introductory L_p material using sentences and paragraphs.
Rename problems section for asymptotics
Rewrite convergence in probability material

Revises and streamlines the convergence in probability and WLLN
material.
Rewrite and move almost sure convergence material

This commit cuts the computer material for almost sure convergence
and rewrites the text in paragraphs and sentences.  It also moves
this material from the asymptotics section to the fundamental
probability theory section, since almost sure convergence plays very
little role in first year econometrics.
Rewrite CLT material

This commit rewrites and streamlines the CLT section, mostly by switching
from a rough outline format to paragraphs.
Rewrite and merge linear regression asymptotics and heteroskedasticity

This commit moves the white-standard-errors material into the asymptotics
document and merges it with the linear regression asymptotics.  It also
rewrites the linear regression asymptotics to use sentences and paragraphs
instead of a loose outline.
Rewrite asymptotics results for general estimators

This commit moves the discussion of general asymptotic properties
of estimators into a single file.  It also converts the results into
paragraphs.
Rewrite bootstrap text and add Sweave code

This commit rewrites the bootstrap material to use paragraphs
and coherent trains of thought instead of a loose outline form.
The commit also moves the example code into an Rnw (sweave) file
so that it generates graphs on the fly.
Edit and move GLS material

This commit moves the GLS material from the linear regression
document; "infeasible" GLS is moved to the section on finite
sample properties of the OLS estimator and "feasible" GLS is
now in the asymptotics document with the rest of the discussion
of heteroskedasticity.

Both sections have been tightened up and put into paragraphs
and sentences.
Spellcheck asymptotics documents
Merge pull request #24 from grayclhn/edit-asymptotics-text

A sequence of edits to the "asymptotics" document to turn it from a loose outline of lecture notes into paragraphs, sentences, etc.